Image pickup device and image pickup optical system

ABSTRACT

An optical system enables images of a wide range of natural subjects to be well reproduced with their colors, and provides an image pickup system including, at least, an image pickup optical system, an electronic image pickup device having three or more different spectral characteristics to obtain a color image, and a controller for implementing signal processing or image processing on the basis of an output from the electronic image pickup device. The optical element that takes part in the determination of a focal length in said image pickup system includes an optical element making use of a refraction phenomenon alone. The  400 -nm wavelength input/output ratio is 10% or less with respect to an input-output ratio for a  400 -nm to 800-nm wavelength at which an output signal strength ratio with respect to an input quantity of light is highest when the input quantity of light is defined by the quantity of a light beam emanating from the same object point and entering the image pickup optical system and the output signal strength is defined by the strength of a signal produced from the controller in response to the light beam.

The claims of this application benefit of Japanese Patent ApplicationNos. 11-194400, 11-325685, 2000-021860 and 2000-075690 filed in Japan onJul. 8, 1999, Nov. 16, 1999, Jan. 26, 2000 and Mar. 17, 2000,respectively, the content of which are incorporated by this reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to an image pickup system and animage pickup optical system, and more particularly to an image pickupoptical system and electronic image pickup system for forming a subjectimage on the image pickup surface of an electronic image pickup devicesuch as a CCD, which comprises a plurality of pixels having at leastthree different spectral characteristics for obtaining a color image.

An electronic image pickup system using an electronic image pickupdevice is designed to have sensitivity even to wavelengths of 400 nm orless so as to ensure the quantity of light sensible to the electronicimage pickup device. For instance, when the quantity of light sensed bythe electronic image pickup device is small, gamma characteristics areoften controlled to make the output from the photoelectric convertershigher than the input thereto upon image reproduction. If, in this case,the spectral state of the subject is substantially constant, noparticular problem arises. However, when the energy of wavelengths(e.g., h-line) in the vicinity of 400 nm is large with respect to thatof, for instance, 450 nm or g-line, a problem arises; for instance, theblue tint of the reproduced image is more stressed than when actuallyseen by the human eyes. The reason is that while the sensitivity of thehuman eyes to the short wavelength side of the visible range isconsiderably low, yet such short wavelengths are reproduced by anelectronic image pickup device in colors perceptible to the human eyes,because the sensitivity of the device to the short wavelength range isrelatively high.

For recently developed digital cameras comprising a ever-larger numberof pixels, on the other hand, it is required to achieve drastic size andcost reductions. With this, image pickup optical systems, too, are nowrequited to have ever-higher performance and ever-higher zooming andother functions with size and cost reductions. To achieve higherperformance, it is required to increase the image-formation capabilityof a system all over the wavelength range to which the system issensible. In the present disclosure, changes in the image-formationcapability due to wavelengths are called chromatic aberrations. Ingeneral, the chromatic aberrations are corrected making use of the factthat the rate (dispersion) of change of the index of refraction withrespect to wavelengths differ from material to material. For instance,an optical system having a positive focal length is designed to makecorrection for the chromatic aberrations by using a material of smalldispersion for an optical element having positive refracting power and amaterial of large dispersion for an optical element having negativerefracting power.

When the chromatic aberrations are corrected by using a combination ofoptical elements as mentioned above, it is required to take not only thechromatic aberrations but also the image-formation capability of thewhole image pickup surface into consideration; for instance, it isrequired to increase the number of optical elements. For a zoom lenssystem of the type that the focal length of the system is varied byvarying the separations between a plurality of lens groups comprising alens group having a positive focal length and a lens group having anegative focal length, more complicated combinations of optical elementsare required. In this case, when a refracting type of optical element(lens) is formed using a glass or plastic material, the index ofrefraction increases, sometimes drastically, as the wavelength changesfrom a long wavelength side to a short wavelength side, althoughdepending on the material used.

FIG. 84 is illustrative of how the refractive index of two single lenseswhose refracting power (the reciprocal of the focal length) becomes 1 at550-nm wavelength change due to wavelengths. It is here noted that thesingle lenses are constructed using a typical vitreous material and amaterial called an ultra-low dispersion material. FIG. 85 isillustrative of the amount of displacements on the basis of 500 nm ofthe back focal position of an optical system constructed only of ageneral refraction type optical element, with wavelength as abscissa anddisplacement as ordinate. As can be seen from FIG. 84, the refractingtype optical element shows a similar power change tendency with respectto wavelength, irrespective of whether it is formed of a normal materialor an ultra-low dispersion material. Thus, the axial chromaticaberration of an image pickup optical system constructed of a refractingoptical element formed of a material in the practical range has aV-shaped form as shown in FIG. 85; an image is formed on the same pointat only two wavelengths with the chromatic aberrations becoming largeboth on the short and long wavelength sides. On the short wavelengthside in particular, there is a large chromatic aberration change. Toreduce such chromatic aberration changes, it is proposed to make use offluorite and a special-purpose glass such as an ultra-low dispersionglass. However, this special glass, too, has such characteristics asshown in FIG. 84; in other words, it is difficult to reduce thechromatic aberration change on the short wavelength side to asufficiently low level. When this glass is used for an electronic imagepickup device, colors of short wavelengths appear together withchromatic aberrations, and so offer an unnatural “color running”problem.

In JP-A 10-170822 as one prior art, it is proposed to reduce thechromatic aberration changes on the short wavelength side by use of adiffractive optical element. According to this publication, chromaticaberrations due to the light used are corrected making use of thereciprocal dispersion of the diffractive optical element. In thediffractive optical element, however, diffracted light other than theused light appears in the form of unnecessary light, which is in turnresponsible for ghosts and flares. In this publication, the wavelengthrange is limited, whereby the influence of unnecessary light on thediffractive optical element is reduced.

However, this unnecessary light reaches the image-formation planediscontinuously (independently) with respect to the used light. In thespectral wavelength characteristics, too, the unnecessary light isdiscontinuous with respect to the used light. In this publication,unnecessary light having no relation to normal image-formation (by theused light) is reduced making use of its wavelength characteristicdifference. To obtain good images, it is thus required to largely reducethe strength of the image due to unnecessary light. For instance, asystem hardly sensible to 420 nm is proposed.

However, 420 nm has an influence on the sense of sight of the human ingeneral and the perception of colors in particular. In view of colorreproduction, reducing this wavelength is tantamount to reducing a shortwavelength component than required, leading to a possible impairment ofnatural color reproduction. Thus, a problem with the technique set forthin this publication is that it is difficult to make a reasonabletradeoff between high color reproducibility and flare removal, becausethe short wavelength range having an influence on the sense of sight ofthe human must be largely cut off so as to make the influence ofunnecessary light unobtrusive.

With conventional design with weight given to an intermediate wavelengthregion in the visible range, it is impossible to make perfect correctionfor chromatic aberrations at both ends of the visible range, and thoseon the short wavelength side in particular. For this reason, when theimage of a high-contrast subject is picked up, the colors of shorterwavelengths are not only stressed but also color flares of brighterblues occur at the boundary of light and shades.

For recently developed digital cameras comprising a ever-larger numberof pixels, it is required to achieve drastic size and cost reductions,as already mentioned. With this, image pickup optical systems, too, arenow required to have ever-higher performance and ever-higher zooming andother functions with size and cost reductions. Especially for increasingthe number of pixels and achieving size reductions, it is required todecrease the area of each pixel of the image pickup device. This meansthat it is required to increase on a per-unit-area basis the quantity oflight subjected to photoelectric conversion by an image pickup device.In other words, it is required to make the S/N ratio of the devicefavorable, maintain the sensitivity of the device to a dark subject andmake short device exposure time

To obtain a color image, a color filter having such a filter arrangementas shown in FIG. 2 or 3 is located in front of the image pickup deviceso as to achieve a photoelectric conversion device having at least threedifferent wavelength characteristics. The filter shown in FIG. 2 is ofthe type called a primary color filter comprising red (R), green (G) andblue (B) filter elements. The respective wavelength characteristics ofthese filter elements are shown in FIG. 4. The filter shown in FIG. 3 isof the type called a complementary color filter comprising cyan (C),magenta (M), yellow (Ye) and green (G) filter elements. The respectivewavelength characteristics of these filter elements are shown in FIG. 5.When the complementary color filter is used as the filter, the filteredlight is converted by a controller 4 to R, G and B according to thefollowing processing:

for luminance signalsY═|G+M+Ye+C|*¼for color signalsR−Y=|(M+Ye)−(G+C)|B−Y=|(M+C)−(G+Ye)|

Both the primary color filter and the complementary color filter are notsensible to the human eyes. In many cases, an IR cutoff filter havingsensitivity to the image pickup device and capable of cutting off lightof wavelengths of about 700 nm or greater (infrared cutoff filter) islocated in an optical system. Most of IR cutoff filters are designed tocut off wavelengths of 700 nm or greater, and so their transmittancewith respect to the vicinity of 600 nm becomes worse, as shown in FIG.68.

With the primary color filter, it is easy to carry out processing forcolor reproduction. When the complementary color filter with an R, G andB conversion process is used, an output of R signals (for reddevelopment) is produced with respect to the input of the bluewavelength range (a wavelength of about 400 nm to about 430 nm in FIG.11) upon conversion from the complementary color filter to R, G and B.

For this reason, the primary color filter is mainly used for digitalcameras required to have a large number of pixels and high imagequality. Sometimes, the complementary color filter is used for an imagepickup system less likely to produce chromatic aberrations. The “imagepickup system less likely to produce chromatic aberrations” isunderstood to include an image pickup system wherein the number ofpixels is so reduced that the aberrations of a phototaking lens havelittle or no influence on image quality, and an image pickup system withinherently reduced chromatic aberrations (this may be achieved byincreasing the F-number of the system, decreasing the magnification of azoom lens in the case of a zoom lens system, using a vitreous material(e.g., fluorite) that costs much or is of poor productivity, increasingthe number of lens elements, and increasing the length of the system.

With the primary color filter, it is easy to carry out processing forcolor reproduction. However, the quantity of light entering each pixelis small (because the wavelength range of light entering each pixel isnarrow). In the primary color filter, only G has sensitivity to green(light in the wavelength range of about 500 nm to about 550 nm) that isa significant determinant for image resolution. For this reason, theprimary color filter is designed in such a way that the ratio of R, Gand B pixels is set at 1:2:1, thereby regulating the ratio of pixelshaving a significant influence on the determination of image resolutionto 50%.

When such a primary color filter is used, the quantity of light enteringeach pixel is small, and so problems arise in connection with S/N andexposure time as pixel size becomes small. The pixels having aninfluence on image resolution are barely 50%; there is a problem that itis impossible to take full advantage of the large number of pixels,thereby achieving high image quality.

SUMMARY OF THE INVENTION

In view of such problems as explained with reference to the prior art, aprimary object of the present invention is to provide an optical systemwhich enables the images of a wide range of natural subjects to be wellreproduced with their colors although its construction is simplified. Inother words,

a) one particular object of the invention is to reduce or eliminate thecontribution of wavelengths—which are virtually insignificant to thehuman sense of sight—to the determination of the colors of a reproducedimage, and

b) another particular object of the invention is to reduce or eliminatea reproduced image deterioration due to wavelengths which are virtuallyinsignificant to the human sense of sight.

Yet another object of the invention is to provide an electronic imagepickup system and an image pickup optical system which, albeit beingsimple in construction, enable the images of a wide range of naturalsubjects to be well reproduced with reduced color flares.

A further object of the invention is to provide an optical system which,albeit being simple in construction, enables a satisfactory image to bereproduced with its colors. A further object of the invention is toprovide an optical system suitable for reducing the cost and size of adigital camera, yet with an increased number of pixels.

According to the first embodiment of the first aspect of the presentinvention, there is provided an image pickup system comprising, atleast, an image pickup optical system, an electronic image pickup devicehaving three or more different spectral characteristics to obtain acolor image and a controller for implementing signal processing or imageprocessing on the basis of an output from the electronic image pickupdevice, characterized in that:

an optical element that takes part in the determination of a focallength in said image pickup system is made up of an optical elementmaking use of a refraction phenomenon alone, and

a 400-nm wavelength input/output ratio is 10% or less with respect to aninput/output ratio for a 400-nm to 700-nm wavelength at which an outputsignal strength ratio with respect to an input quantity of light ishighest with the proviso that said input quantity of light is defined bythe quantity of a light beam emanating from the same object point andentering said image pickup optical system and said output signalstrength is defined by the strength of a signal produced from saidcontroller in response to said light beam.

The action of the image pickup system according to the first embodimentof the first aspect of the present invention is explained. For theoptical element that takes part in the determination of a focal lengthin the image pickup optical system, an optical element making use of therefraction phenomenon alone is used. When a diffractive optical elementis used as the optical element taking part in the determination of afocal length, effective-order chromatic aberrations may be wellcorrected. However, unnecessary light forms different images on both thelong and short wavelength sides of a wavelength range virtuallysensitive to the human eyesight, resulting in overall drastic imagedeterioration. Thus, the image pickup optical system uses a refractingelement alone; that is, the image pickup optical system does not use anydiffractive optical element, so that the nature of the image in thewavelength range of interest can be gradually changed. Note that asystem comprising an optical element that harnesses a plurality of lightbeams produced by a diffraction phenomenon, for instance, a low-passfilter, too, is embraced in the first embodiment of the first aspect ofthe invention.

In the first embodiment of the first aspect of the present invention,the 400-nm input/output ratio should be 10% or less with the respect tothe input/output ratio for the 400-nm to 700-nm wavelength at which theoutput signal strength ratio with respect to the input quantity of lightis highest. The occupation of wavelengths of 400 nm or less in thespectral luminous efficiency is about 0.01%, and the occupation in thespectral luminous efficiency of a color matching function z for a 10°visual field in the CIE 1964 XYZ colorimetric system is about 0.6%. Onthe other hand, the occupation in the spectral luminous efficiency of acolor matching function x for a 10° visual field in the CIE 1964 XYZcalorimetric system is about 0.1%. Unless this point is satisfied, thereis an alienation between the colors of an object as directly observedand the colors of an object image reproduced through an image pickupdevice, especially when the energy of wavelengths of 400 nm or less isrelatively higher than that of the rest. This alienation makes thecolors of the reproduced image unnatural. More preferably, the 400-nmwavelength input/output ratio should be 5% or less, and especially 2% orless. For color vs. wavelength relations and the color matchingfunctions for the 100 visual field in the CIE 1964 XYZ calorimetricsystem, for instance, see Mitsuo Ikeda, “THE FOUNDATIONS OF COLORENGINEERING”, ASAKURA SHOTEN.

It is noted that the “electronic image pickup device having three ormore different spectral characteristics to obtain a color image” usedwith reference to the first image pickup system according to the firstaspect of the present invention refers to an imaging device designed forthe purpose of forming images, and so does not refer to an imagingdevice designed for AE (automatic exposure) or AF (automatic focusing),which device provides no direct image formation. In this context, it isunderstood that any imaging device for the purpose of forming images,with AE or AF functions added thereto, is embraced in the first imagepickup system.

According to the second embodiment of the first aspect of the presentinvention, the first image pickup system is further characterized inthat a 420-nm wavelength input/output ratio is 10% or greater withrespect to the input/output ratio for the 400-nm to 700-nm wavelength atwhich the output signal strength ratio with respect to the inputquantity of light is highest.

The action of the second image pickup system according to the firstaspect of the present invention is now explained. The occupation ofwavelengths in the vicinity of 420 nm (415 nm to 425 nm) in the spectralluminous efficiency is about 1.6%, and the occupation in the spectralluminous efficiency of the color matching function z for the 10° visualfield in the CIE 1964 XYZ calorimetric system is about 12%. On the otherhand, the occupation in the spectral luminous efficiency of the colormatching function x for the 100 visual field in the CIE 1964 XYZcalorimetric system is about 2.6%. Although this wavelength range has alimited influence on the spectral luminous efficiency, yet it has asufficient influence on the determinant of tints. When the 420-nminput/output ratio is less than 10%, it is impossible to achieve anyreproduction of natural colors. The 420-nm input/output ratio should bepreferably at least 15%, and more preferably at least 20%.

According to the third embodiment of the first aspect of the presentinvention, there is provided an image pickup system comprising, atleast, an image pickup optical system and an electronic image pickupdevice having three or more different spectral characteristics to obtaina color image, characterized in that:

an optical element that takes part in the determination of a focallength in said image pickup system is made up of an optical elementmaking use of a refraction phenomenon alone, and

a 400-nm wavelength input/output ratio is 6% or less with respect to aninput/output ratio for a 400-nm to 700-nm wavelength at which an outputsignal strength ratio with respect to an input quantity of light ishighest with the proviso that said input quantity of light is defined bythe quantity of a light beam emanating from the same object point andentering said image pickup optical system and said output signalstrength is defined by the strength of a signal produced from the imagepickup device in response to said light beam.

The action of the third image pickup device according to the firstaspect of the present invention is now explained. When signals producedfrom the image pickup device are weak, the input/output ratio is oftenaltered through gamma correction or the like at a controller. Ifrequired, signal processing and image processing at the controller maybe altered by software changing. The third image pickup system isconstructed with such alteration in mind, so that color reproducibilitycan be improved at outputs from the image pickup optical system andimage pickup device. It is here noted that the 400-nm wavelengthinput/output ratio should be preferably 3% or less, and more preferably1.2% or less.

According to the fourth embodiment of the first aspect of the presentinvention, the third image pickup system is further characterized inthat a 420-nm wavelength input/output ratio is 6% or greater withrespect to the input/output ratio for the 400-nm to 700-nm wavelength atwhich the output signal strength ratio with respect to the inputquantity of light is high.

The action of the fourth image pickup device is the same as that of thesecond image pickup device. The 420-nm wavelength input/output ratioshould be preferably 9% or greater, and more preferably 12% or greater.

According to the fifth embodiment of the first aspect of the presentinvention, there is provided an image pickup system comprising, atleast, an image pickup optical system and an electronic image pickupdevice having three or more different spectral characteristics to obtaina color image, characterized in that:

an optical element that takes part in the determination of a focallength in said image pickup system is made up of an optical elementmaking use of a refraction phenomenon alone, and

-   -   a spectral transmittance from an entrance portion of said image        pickup optical system to an entrance portion of said electronic        image pickup device is such that the ratio of a 400-nm        wavelength transmittance with respect to a transmittance for a        wavelength of 400 nm to 700 nm at which the highest        transmittance is obtained is 15% or less.

The action of the fifth image pickup system is now explained. Inconsideration of cost, the image pickup device is a constituting memberthat benefits from the greatest effects of the economies of scale. Inview of cost and production, it is thus preferable to achieve an imagepickup device that can be commonly mounted on an image pickup systemdesigned to phototake a subject in a room substantially free from lightbeams in the vicinity of 400 nm and an image pickup system wherein thereis no strong demand for the natural color-match reproducibility on thepremise that color correction should be made for each pixel duringdisplaying, printing or the like. In both types of image pickup systems,how the quantity of light is ensured takes precedence over colorreproducibility, etc. With the fifth image pickup system, it is possibleto obtain images with improved color reproducibility even when such animage pickup device is used under a light source containing someconsiderable short wavelengths, for instance, under solar rays, becausethe 400-nm wavelength transmittance is limited with respect to thespectral transmittance from the entrance portion of the image pickupoptical system to the entrance portion of the electronic image pickupdevice. It is here noted that the ratio of 400-nm wavelengthtransmittance should be preferably 8% or less, and more preferably 3% orless.

According to the sixth embodiment of the first aspect of the presentinvention, the fifth image pickup system is further characterized inthat the ratio of 420-nm wavelength transmittance with respect to thetransmittance for the wavelength of 400 nm to 700 nm at which thehighest transmittance is obtained is 15% or greater.

The action of this sixth image pickup system is the same as that of thesecond image pickup system. It is noted that the ratio of 420-nmwavelength transmittance should be preferably 20% or greater, and morepreferably 25% or greater.

According to the seventh embodiment of the first aspect of the presentinvention, the fifth or sixth image pickup system is furthercharacterized in that at least one of the three different spectralcharacteristics that the electronic image pickup device possesses so asto obtain a color image has two peak wavelengths, each of highsensitivity, between which there is a wavelength having a sensitivity of50% or less to the sensitivities of the two peak wavelengths. The actionof the seventh image pickup system is now explained. The image pickupdevice in the seventh image pickup system is a color-compatible imagepickup device using a so-called complementary color filter. Thecomplementary color filter is advantageous over a primary color filterin that the quantity of light can be easily ensured. For the seventhimage pickup system, at least one filter having two peak wavelengths,each of high sensitivity, should be located. Requirements for the filterare that the peak-to-peak trough be kept as constant as possible and thepeaks be reached with a sharp rising edge. When the sensitivity to about400 nm is decreased from the peak sensitivity on a short wavelengthside, the construction of the filter becomes complicated. In addition,when the sensitivity to 420 nm is ensured to a certain degree, theconstruction of the filter becomes more complicated. According to thisseventh embodiment, it is thus possible to provide an image pickupsystem that makes it easy to ensure light quantity and is of generalversatility, because the 400-nm or 400-nm and 420-nm wavelengthtransmittance is restricted before the wavelengths enter the imagepickup device.

According to the eighth embodiment of the first aspect of the presentinvention, there is provided an image pickup optical system detachablymounted on an image pickup system comprising an electronic image pickupdevice having three or more different spectral characteristics so as toobtain a color image, characterized in that:

an optical element that takes part in the determination of a focallength in said image pickup optical system is made up of an opticalelement making use of a refraction phenomenon alone, and

the spectral transmittance of said image pickup optical system is suchthat the ratio of 400-nm wavelength transmittance thereof with respectto the transmittance thereof for a wavelength of 400 nm to 700 nm atwhich the highest transmittance is obtained is 15% or less.

The action of the image pickup optical system according to the eighthembodiment of the first aspect is now explained. Such an image pickupoptical system can be mounted on a variety of image pickup systems withhigh color reproducibility. It is noted that the ratio of 400-nmwavelength transmittance should be preferably 8% or less, and morepreferably 3% or less.

According to the ninth embodiment of the first aspect of the presentinvention, the image pickup optical system according to the eighthembodiment is further characterized in that the ratio of a 420-nmwavelength transmittance thereof with respect to the transmittancethereof to a wavelength of 400 nm to 700 nm at which the highesttransmittance is obtained is 15% or greater.

It is noted that the ratio of 420-nm wavelength transmittance should bepreferably 20% or greater, and more preferably 25% or greater.

According to the tenth embodiment of the first aspect of the presentinvention, there is provided an image pickup system comprising anelectronic image pickup device having three or more different spectralcharacteristics to obtain a color image, a controller for carrying outsignal processing or image processing on the basis of an output fromsaid electronic image pickup device and a mount for enabling an imagepickup optical system for guiding an outside image to said electronicimage pickup device to be detachably mounted on said image pickupsystem, characterized by further comprising a wavelength range controlmeans for allowing a 400-nm wavelength input/output ratio to be 10% orless with respect to an input/output ratio for a wavelength of 400 nm to700 nm at which the ratio of an output signal strength with respect toinput light quantity is highest with the proviso that said input lightquantity is defined by the quantity of an incident light beam and saidoutput signal strength is defined by the strength of a signal producedfrom the controller in response to said incident light beam.

The action of the tenth image pickup system is now explained. Even whenvarious image pickup optical systems are mounted on this tenth imagepickup system, satisfactory color reproduction is achievable. It isnoted that the 400-nm wavelength input/output ratio should be preferably5% or less, and more preferably 2% or less.

According to the eleventh embodiment of the first aspect of the presentinvention, the eleventh image pickup system is further characterized inthat said wavelength range control means allows a 420-nm wavelengthinput/output ratio to be 20% or greater with respect to the input/outputratio for a wavelength of 400 nm to 700 nm at which the ratio of theoutput signal strength with respect to the input light quantity ishighest.

According to the twelfth embodiment of the first aspect of the presentinvention, the tenth or eleventh image pickup system is furthercharacterized in that the wavelength range control means is a filterinterposed between the electronic image pickup device and the mount.

The action of the twelfth image pickup system is now explained. By usinga mosaic filter with the image pickup device or locating other filter onthe entrance surface of the image pickup device, it is thus possible toobtain an image with improved color reproducibility yet without makingsignal processing complicated.

According the thirteenth embodiment of the first aspect of the presentinvention, any one of the first through seventh image pickup systems isfurther characterized in that when the image pickup optical system isfocused at 70% of an effective screen thereof on an infinite objectpoint, chromatic aberrations in meridian section at a 400-nm wavelengthare equivalent in size to four or more pixels.

The action of the thirteenth image pickup system is now explained. Therefracting power of an optical element used with an image pickup opticalsystem varies with changing wavelength. The so-called glass or plasticmaterials have increasing power as wavelength becomes short. In otherwords, image-formation capability varies with changing wavelength. Oneindex to how sharply refracting power changes due to wavelength is anAbbe number. In general, lenses with varying Abbe numbers are located inthe form of a positive and a negative lens for the purpose of reducingthe changes in the image-formation capability due to changingwavelength. Unlike microscopes or the like, an image pickup systemhaving a relatively wide field angle such as a general-purpose digitalcamera is required to have its image-formation capability in compliancewith large wavelength changes while the image-formation capability ismaintained at the desired level. However, the construction of an imagepickup optical system does not only become complicated but also anexpensive material of poor processability is needed, resulting in theneed of meeting a high level of fabrication precision.

According to the thirteenth embodiment of the first aspect of thepresent invention, the optical system is designed in such a way thatwhen focused on an infinite object point in the range of 70% of theeffective screen, the chromatic aberrations in meridian section at a400-nm wavelength are equivalent in size to four or more pixels. It isthus possible to provide an optical system of simplified construction,which makes it possible to enhance its image-formation capability in thewavelength region taking part in image formation.

In this regard, an account is given of the limitation that the chromaticaberrations in meridian section are equivalent in size to four or morepixels. Here consider the state where the image pickup system is focusedon an infinite object point (i.e., the state where the image pickupsystem is focused through an autofocusing mechanism on a nearly infiniteobject point or it is focused on a nearly infinite object point in amanual focusing mode set on an infinite memory, or the state where thepeak of an axial PSF (point spread function) strength at d-line (587.6nm) is maximized with respect to an infinite object point on an opticalaxis. Then, the chromatic aberrations are defined by a size δ onmeridian section, which accounts for at least 1.6% of the maximum valueof the PSF strength at a specific wavelength. In other words, theaforesaid limitation means that the size δ (400) at 400-nm wavelength isequivalent to four or more pixels.

Also assume the length from the center of the image pickup surface to amaximum effective image height to be equal to 1. Then, the range of 70%of the effective screen is defined by the inside of a circle, the radiusof which is 7/10 of that length.

According to the fourteenth embodiment of the first aspect of thepresent invention, the thirteenth image pickup system is furthercharacterized in that chromatic aberrations for a wavelength of 435 nmto 600 nm are equivalent to three or less pixels in the range of 70% ofthe effective screen.

The action of the fourteenth image pickup system is now explained. Withthis construction, it is possible to provide an image pickup opticalsystem wherein the image-formation capability change due to wavelengthis on a practically acceptable level. It is here noted that a certainimage pickup optical system designed to be detachable from an imagepickup system, if it can be mounted on the image pickup system for use,is also embraced in the present invention.

Here let D represent the effective diagonal length of the electronicimage pickup device, and δ(400) and δ(420) stand for chromaticaberrations at 400-nm wavelength and 420-nm wavelength as found in therange of 70% of the effective screen, respectively. It is thenpreferable to satisfyδ(400)/D>2.0×10⁻³It is more preferable to satisfyδ(420)/D<1.5×10⁻³

While the chromatic aberrations for 400-nm wavelength and 420-nmwavelength have been discussed, it is understood that even when thechromatic aberrations for 400-nm wavelength are replaced by those forh-line (404.7 nm) and the chromatic aberrations for 420-nm wavelengthare replaced by those for g-line (435.8 nm), the same effects areachievable.

Referring to the chromatic aberrations of magnification, it ispreferable that the distance between the peak of a d-line spot and thepeak of a g-line spot is equivalent to seven or less pixels all over theeffective screen of the electronic image pickup device. More preferablyin this case, the distance between the d-line and the g-line should beequivalent to ten or more pixels.

Alternatively, let Δdh, Δdg and D represent the distance between thepeaks of d- and h-lines, the distance between the peaks of d- andg-lines and the effective diagonal length of the electronic image pickupdevice. It is then preferable that the following condition is satisfiedwith respect to at least a part of the screen:Δdh/D>6.0×10⁻³More preferably in this case, the following condition should besatisfied with respect to the whole screen:Δdg/D<4.5×10⁻³

Preferably, such optical elements as explained below are located in theimage pickup optical system in each of the thirteenth and fourteenthimage pickup systems, etc.

According to the fifteenth embodiment of the first aspect of the presentinvention, any one of the first through fourteenth image pickup systemsis further characterized in that the image pickup optical systemcomprises an aperture stop, and an optical system portion located on theimage pickup device side with respect to the aperture stop has generallypositive refracting power and comprises at least one negative lens.

The action of the fifteenth image pickup system is now explained. Therequirement for increasing the efficiency of photoelectric conversion oflight beams incident on the image pickup device (or for bringing thesystem close to a telecentric one) is that the optical system portionlocated on the image pickup device side with respect to the aperturestop has generally positive refracting power. The requirement for makingcorrection for spherical aberrations, axial chromatic aberrations andchromatic aberrations of magnification is that the optical system has atleast one negative lens. By meeting these requirements, it is possibleto provide an image pickup optical system of simplified construction,which has improved image-formation capability in the necessarywavelength range. However, note that chromatic aberrations for 400-nmwavelength become large.

According to the sixteenth embodiment of the first aspect of the presentinvention, the fifteenth image pickup system is further characterized inthat the image pickup optical system comprises an aperture stop and anoptical system portion located on the image pickup device side withrespect to the aperture stop comprises, in order from an object sidethereof, a positive lens, a negative lens and a positive lens group or apositive lens, a positive lens, a negative lens and a positive lensgroup.

The action of the sixteenth image pickup system is now explained. Withsuch a lens arrangement, it is possible to reduce the overall length ofthe optical system portion located on the image pickup device side withrespect to the aperture stop. If the power of the negative lens isincreased, it is then possible to enhance this action. At the same,however, aberrations in the vicinity of 400-nm wavelength become large.

According to the seventeenth embodiment of the first aspect of thepresent invention, the fifteenth image pickup system is furthercharacterized in that the image pickup optical system comprises, on theimage pickup device side with respect to the stop, a lens group which,for zooming a wide-angle end to a telephoto end thereof, movesmonotonously from an image side to an object side thereof and comprisesa negative lens.

The action of the seventeenth image pickup system is now explained. Thisarrangement is known to be effective for achieving overall lengthreductions, high zoom ratios and high aperture ratios. In thisarrangement, the group in the rear of the stop, too, makes somecontribution to zooming. In the negative group-preceding type, only thelens group in the rear of the stop contributes to zooming. The negativelens used has functions of making correction for aberrations such asfield curvature as well as chromatic aberrations. To correct aberrationsfor a reference wavelength, some limitations are imposed on the powerand shape of this negative lens. For correction of chromaticaberrations, therefore, it is required to construct the negative lens ofa material having a proper Abbe number. However, this lens has theproperty of varying more largely in the index of refraction aswavelength becomes shorter. It is still difficult to make correction forchromatic aberrations for 400-nm wavelength.

According to the eighteenth embodiment of the first aspect of thepresent invention, the seventeenth image pickup system is furthercharacterized in that in the image pickup optical system, a moving lensgroup is positioned just after the stop.

The action of eighteenth image pickup system is now explained. Thisarrangement is known to be effective for achieving further overalllength reductions, ever higher zoom ratios and ever higher apertureratios. With this negative lens, however, the height of paraxial raysgrows and so chromatic aberrations in the vicinity of 400-nm wavelengthare likely to become large. In particular, the effect of the eighteenthimage pickup system increases with decreasing F-number, becausechromatic aberrations become large.

According to the nineteenth embodiment of the first aspect of thepresent invention, any one of the fifteenth through seventeenth imagepickup systems is further characterized in that the negative lenssatisfies the following conditions:0.2<S R RN /D<2  (3)1.7<ηRN<1.95  (4)20<νRN<30  (5)0.004<ΔθRN<0.05  (6)Here SRRN is the smaller radius of curvature of the negative lens, D isthe diagonal length of the effective image pickup surface of the imagepickup device, ηRN is the index of refraction of the negative lens, νRNis the Abbe number of the negative lens, and ΔθRN is the amount ofdisplacement of the vitreous material of the negative lens in the θg−Fdirection on the basis of a straight line between glass code 511605 andglass code 620363 on a θg−F vs. νd plot of the vitreous material,providing a numerical expression of anomalous dispersion. In thisregard, note that glass code 511605 is a glass product NSL7 made byOHARA Co., Ltd. with a θg-F value of 0.5436 and a νd value of 60.49 andglass code 620363 is a glass product PBM2 made by OHARA Co., Ltd. with aθg-F value of 0.5828 and a νd value of 36.26.

Condition (3) is provided to ensure the f back necessary for the imagepickup optical system. When the upper limit of 2 is exceeded, it isdifficult to ensure the necessary f back. When the lower limit of 0.2 isnot reached, chromatic aberrations for the necessary wavelengths becometoo larger even when conditions (4) to (6) are satisfied. By making anappropriate selection from the vitreous materials capable of satisfyingconditions (4), (5) and (6), it is possible to gain satisfactory controlof chromatic aberrations for the necessary wavelengths. However, theanomalousness of partial dispersion ratios is large, and so the shorterthe wavelength, the more rapidly are chromatic aberrations produced. Itis thus difficult to make correction for aberrations for 400-nmwavelength. The left side of condition (3) should be preferably 0.3 andmore preferably 0.5, and the left side of condition (6) should bepreferably 0.007 and more preferably 0.01.

According to the twentieth embodiment to the first aspect of the presentinvention, any one of the fifteenth through eighteenth image pickupsystems is further characterized in that the optical element ofrefracting power, located nearest to the image side of the image pickupoptical system, is a positive lens.

This arrangement is known to result in overall length reductions.However, the chromatic aberrations of this positive lens are enlargedthrough the optical system portion located on the image pickup deviceside with respect to the positive lens. Chromatic aberrations for 400-nmwavelength are larger than those for 435-nm wavelength for instance, andthis difference is enlarged, producing a large influence on thechromatic aberrations of magnification in particular.

According to the twenty-first embodiment of the first aspect of thepresent invention, the twentieth image pickup system is furthercharacterized in that an air separation between the positive lens and alens located adjacent thereto is variable during zooming. Thisarrangement is preferable because the amount of movement of the lensgroups is reduced during zooming.

According to the twenty-second embodiment of the first aspect of thepresent invention, any one of the fifteenth through twenty-first imagepickup systems is further characterized in that the image pickup opticalsystem is constructed of a zooming system comprising, in order from anobject side thereof, a first group having positive refracting power, asecond group having negative refracting power, a third group havingpositive refracting power and a fourth group having positive refractingpower.

This arrangement is preferable because the amount of movement of thegroups during zooming is reduced, and makes it easy to reduce theoverall length of the system and decrease the F-number of the system.

According to the twenty-third embodiment of the first aspect of thepresent invention, any one of the image pickup systems or image pickupoptical systems according to the first through ninth embodiments,thirteenth and fourteenth embodiments is further characterized in thatthe image pickup optical system has therein a reflecting surface havinga reflectance of 50% or greater at 400-nm wavelength and 10% or less at420-nm wavelength.

The action of the twenty-third image pickup system is now explained. Bylocating in the image pickup optical system a reflecting surface havingan antireflection function at 420-nm wavelength and an increasedreflection function at 400-nm wavelength, it is possible to obtain aclear image.

According to the twenty-fourth embodiment of the first aspect of thepresent invention, the twenty-third image pickup system or image pickupoptical system is further characterized in that the reflecting surfaceis formed of at least two thin films having different refractiveindices, which films are laminated upon one another.

The action of the twenty-fourth image pickup system is now explained. Itis desired that the reflecting surface is formed of a multilayered filmlaminated on the surface of an optical element.

According to the twenty-fifth embodiment of the first aspect of thepresent invention, there is provided an image pickup system comprising,at least, an image pickup optical system, a filter or prism and anelectronic image pickup device having three or more different spectralcharacteristics to obtain a color image, characterized in that:

an optical element that takes part in the determination of a focallength in said image pickup optical system is formed of an opticalelement making use of a refraction phenomenon alone, and

at least one filter or prism has a 400-nm wavelength transmission of 10%or less with respect to the maximum wavelength transmission.

The action of the twenty-fifth image pickup system is now explained. Foran image pickup system, it is often required to locate an infraredcutoff filter, a low-pass filter and an optical path splitter prismtherein. It is preferable to form the filter or prism of a materialhaving a 400-nm wavelength transmittance of 10% or less with respect tothe maximum transmission, because it is unnecessary to use an additionalmember for restricting a 400-nm wavelength light beam. It is noted thatthe 420-nm wavelength transmission should be preferably 40% or greaterwith respect to the maximum transmission wavelength.

According to the twenty-sixth embodiment of the first aspect of thepresent invention, there is provided an image pickup system comprising,at least, an image pickup optical system, an optical path splitter meanslocated in an optical path for said image pickup device to split theoptical path to a finder optical path and a phototaking optical path,and an electronic image pickup device having three or more differentspectral characteristics to obtain a color image, characterized in that:

an optical element that takes part in the determination of a focallength in said image pickup optical system is formed of an opticalelement making use of a refraction phenomenon alone, and

the proportion of a light beam emerging from said optical path splittermeans toward the electronic image pickup device with respect to a lightbeam incident on said optical path splitter means is such that the ratioof a 400-nm wavelength light beam leaving said means with respect to alight beam of the longest wavelength in the range of wavelengths used isless than 1.

The action of the twenty-sixth image pickup system is now explained.Even when the finder is removed off, the quantity of light emanatingfrom the subject often offers no problem. In this case, when more lightbeams of 400 nm or less in wavelength are incident on the finder opticalsystem, there is little or no influence on the perception of colors orimages by the human sense of sight. In the image pickup device, on theother hand, a 400-nm wavelength light beam is treated in the same manneras a 435-nm light beam; that is, there is an influence on the perceptionof colors. Thus, the twenty-sixth image pickup system that permits thegreater portion of the 400-nm wavelength light beam is allocated to thefinder optical system is preferable.

The second aspect of the present invention is now explained.

For an image pickup system such as a camera designed to phototakevisible light areas, it is generally required that an image pickupoptical system be optimized on the basis of the vicinity of anintermediate wavelength in the visible light range. When, at this time,it is intended to obtain satisfactory optical performance all over thevisible light range, extra costs are added to the optical system becauseof the need of using a special vitreous material for correctingchromatic aberrations and increasing the number of lenses.

The purport of the second aspect of the present invention is to achievean image pickup system and an image pickup optical system at low costs,which permit certain degrees of chromatic aberrations and can reducecolor flares down to an unobtrusive level by warning the observer ofcolor flares likely to occur due to chromatic aberrations, reducingcolor flares electrically or placing a wavelength range with prominentchromatic aberrations in an optically unobtrusive state.

According to the first embodiment of the second aspect of the presentinvention, this object is achieved by the provision of an electronicimage pickup system characterized by comprising an electronic imagepickup device having three or more different spectral characteristics toobtain a color image, an image pickup optical system for producingchromatic aberrations and forming a subject image on the image pickupsurface of the electronic image pickup device, a large luminancedifference detecting means for detecting an area where a luminancedifference among certain adjacent pixels of the electronic image pickupdevice reaches or exceeds a certain level, and a warning means forissuing a warning of detection of a certain or greater luminancedifference by the large luminance difference detecting means.

With this arrangement, it is possible for the operator to have animmediate understanding of the fact that the subject is likely toproduce high-contrast color flares. Then, suitable means can be used toreduce such high-contrast color flares, so that images with reduced orunobtrusive color flares can be obtained. For instance, the operator canmove close to the subject, set the camera angle in a follow light modeor use an electronic flash to reduce the luminance difference.

For the warning means, it is acceptable to use a buzzer for soundingbeeps, a warning indicator built in a finder or a liquid crystal displayin a camera body or a flash actuator for reducing luminance differences.

It is understood that a screw coupling mount or other mount on which theimage pickup optical system can be mounted may be used for a lensreplaceable camera.

According to the second embodiment of the second aspect of the presentinvention, there is provided an electronic image pickup systemcharacterized by comprising an electronic image pickup device includinga plurality of pixels having three or more different spectralcharacteristics to obtain a color image and provided for converting animage sensed by said pixels to an electric signal including luminanceand color information and producing said electric signal, an imagepickup optical system for producing chromatic aberrations and forming asubject image on the image pickup surface of said electronic imagepickup device, a large luminance difference boundary detecting means fordetecting a boundary where a luminance difference among certain adjacentpixels of said electronic image pickup device reaches or exceeds acertain level, and a signal processing means for electricallycontrolling said electric signal including luminance and colorinformation in such a way as to reduce color flares due to saidchromatic aberrations in the vicinity of said boundary including acertain or greater level of luminance difference when said certain orgreater level of luminance difference is detected by said largeluminance difference boundary detecting means.

According to the third embodiment of the second aspect of the presentinvention, there is provided an electronic image pickup systemcharacterized by comprising an electronic image pickup device includinga plurality of pixels having three or more different spectralcharacteristics so as to obtain a color image and provided forconverting an image sensed by said pixels to an electric signalincluding luminance and color information and producing said electricsignal, an image pickup optical system for producing chromaticaberrations and forming a subject image on the image pickup surface ofsaid electronic image pickup device, a correct exposure calculatingmeans for calculating a correct exposure value for a phototaking area onsaid electronic image pickup device, a large luminance differenceboundary detecting means for detecting a boundary having a largeluminance difference by detecting a pixel having an exposure levelsaturated by underexposure of 2 EV or less with respect to said correctexposure and/or an unsaturated pixel adjacent to said saturated pixel,and a signal processing means for electrically controlling said electricsignal including luminance and color information in such a way as toreduce color flares due to said chromatic aberrations in the vicinity ofsaid boundary detected by said large luminance difference boundarydetecting means.

A high-luminance subject portion such as the sky or illuminations existsin the form of an area where the exposure level is saturated even byunderexposure of 2 EV or less with respect to correct exposure, and sohigh-contrast areas adjacent thereto are likely to give rise to colorflares. However, if the electronic image pickup system according to thesecond aspect of the present invention is constructed as in the thirdembodiment thereof, it is then possible to reduce color flares caused bysuch areas.

In the second or third image pickup system according to the secondaspect of the present invention, it is preferable to use atwo-dimensional area photometric sensor as the large luminancedifference boundary detecting means.

If the two-dimensional area photometric sensor is used, it is thenpossible to detect a high-luminance area and low-luminance areasadjacent thereto on the image pickup surface and thereby find out a zonehaving a large luminance difference, so that color flares can be reducedby the signal processing means operated on the basis of the results.

It is also preferable to locate a plurality of pixels provided withsensitivity reducing means on the image pickup surface of the electronicimage pickup device, so that the boundary can be detected by use oflight sensing signals from those pixels.

This arrangement enables the image pickup device and two-dimensionalarea photometric sensor to be constructed in a monolithic form, which inturn makes it possible to reduce the size of the image pickup device.Through luminance information obtained from high-sensitivity pixels andlow-sensitivity pixels, it is also possible to obtain an area where theexposure level is saturated and areas adjacent thereto.

For the sensitivity reducing means, it is possible to use an ND filter,etc.

If the color saturation of an area of the image pickup surface in thevicinity of the boundary is reduced by the signal processing means, itis then possible to reduce color flares to an unobtrusive “colorrunning” level.

If the area to be reduced in color saturation is composed of one through50 pixels found around the boundary, it is then possible to place signalprocessing quantity and color correction effect in a well balancedstate. With less than one pixel, it is impossible to make perfectcorrection for color flares. With more than 50 pixels, the signalprocessing quantity becomes too much. In the second or third imagepickup system according to the second aspect of the present invention,it is further preferable that the signal processing means is used toapproximate the chromaticity of the boundary and an area adjacent to theboundary and on a dark side of lower luminance to the chromaticity of adark area spaced away from the boundary toward the dark side by at leasta certain number of pixels, thereby eliminating color flares to anunobtrusive “color running” level.

If the aforesaid dark area is defined by 2 through 50 pixels as countedfrom the boundary to the dark side, it is possible to place signalprocessing quantity and color correction effect in a well-balancedstate. With less than 2 pixels, it is impossible to make perfectcorrection for color flares. With more than 50 pixels, the signalprocessing quantity becomes too much.

In the first to third embodiments of the second aspect of the presentinvention, it is preferable that the image pickup optical system forproducing chromatic aberrations satisfies the following condition (11):(Lh−Ld)/F _(min)≧2P  (11)where P and F_(min) are the minimum pixel pitch and minimum F-number forthe electronic image pickup device, and Lh is the absolute value ofspherical aberrations for a h-line (404.7 nm) marginal ray and Ld is theabsolute value of spherical aberration for a d-line (587.56 nm) marginalray when the F-number is F_(min).

In the first to third embodiments of the second aspect of the presentinvention, it is preferable that the image pickup optical system forproducing chromatic aberrations satisfies the following condition (12):|Sh|≧2P  (12)where P is the minimum pixel pitch for the electronic image pickupdevice, and Sh is the amount of transverse chromatic aberration ofmagnification for h-line with respect to d-line at any one of the imageheight ratios of 0.9, 0.7 and 0.5 with respect to the maximum imageheight.

When both the lower-limit 2P values in conditions (11) and (12) are notreached, it is possible to dispense with any signal processing becausechromatic aberrations themselves become small.

In the second aspect of the present invention, condition (11) may bereplaced by the following-condition (11′):(Lh−Ld)/F _(min)>4P  (11′)

In the second aspect of the present invention, condition (11′) may alsobe replaced by the following condition (11″):(Lh−Ld)/F _(min)≧6P  (11″)

In the second aspect of the present invention, condition (12) may bereplaced by the following condition (12′):|Sh|≧3P  (12′)

In the second aspect of the present invention, condition (12′) may alsobe replaced by the following condition (12″):|Sh|≧5P  (12″)

In the second aspect of the present invention chromatic aberrationsbecome larger in the order of conditions (11′), (11″), (12′) and (12″).By satisfying these conditions, however, electric correction isachievable, resulting in the achievement of reductions in the size ofthe optical system.

How color flares due to chromatic aberrations are optically reducedaccording to the second aspect of the present invention is nowexplained.

FIG. 21 is a conceptual representation of the image pickup opticalsystem designed to optically reduce color flares according to the secondaspect of the present invention. An image pickup optical system 101comprises a filter 103, etc. as a wavelength correction means. A lightbeam passing through the image pickup optical system 101 forms a subjectimage on an image pickup device 102. Then, an image including the wholevisible light range is formed on an image plane 104. It is noted thathow the image is formed with respect to the center of the image plane isjudged on the basis of a spherical aberration diagram.

FIG. 22 is a spherical aberration diagram for the image pickup opticalsystem of FIG. 21. In FIG. 22, Lλ is the F-number upon stop in, i.e.,the absolute value of a difference between a paraxial image point andthe position of intersection of each wavelength marginal ray having themaximum height of incident ray with an optical axis at the minimumF-number or F_(min) or, in another parlance, the absolute value of theamount of spherical aberrations. If λ is d-line (587.56 nm), then theabsolute value of the amount of d-line spherical aberration isrepresented by Ld.

In the aberration diagram of FIG. 22, Ld and Lλ indicate the amount of afocal point displacement at the maximum height of incident ray, and FIG.23 is illustrative of how the focal position displacement is seen in asectional view of the back focal point portion of the image pickupoptical system 101.

In FIG. 23, a solid line refers to a d-line marginal ray at the maximumheight of incident ray, and a broken line indicates a marginal ray of anarbitrary wavelength λ at the maximum height of incident ray. Then, thedisplacement of each wavelength with respect to the paraxial image plane104 is perceived in the form of color flares on the paraxial imageplane.

In FIG. 23, Ld/F_(min) and Lλ/F_(min) indicate the diameters of flareswith an optical axis 105 on the paraxial image plane 104 at the center.

A large difference between Ld/F_(min) and Lλ/F_(min) makes color flareslikely to occur. It is difficult to make correction for chromaticaberrations on a shorter wavelength side with respect to d-line. Toachieve a low-cost image pickup optical system, therefore, it isrequired to keep chromatic aberrations undercorrected on the shorterwavelength side.

For the image pickup optical system according to the second aspect ofthe present invention, it is thus required that the difference betweenLd/F_(min) and Lλ/F_(min) be 0.05 mm. Here let λ1 represent a wavelengthwhere the following condition (13) is satisfied:(Lλ−Ld)/F _(min)=0.05 mm  (13)To allow λ1 to exist within a wavelength range of d-line or shorter towhich the electronic image pickup device is sensitive, permit d-line atwhich good images are obtainable to ensure the light quantity needed forimage formation and reduce the light quantity for wavelength λ1 leadingto color flares, a wavelength λc whose transmittance is a half-value ofd-line transmittance satisfies the following condition (14):λ1≦λc≦d-line (587.56 nm)  (14)

With this arrangement, it is possible to ensure sufficient lightquantity in the vicinity of d-line at which satisfactory image-formationcapability is obtainable, and reduce light quantity for wavelength λ1responsible for color flares. According to the second aspect of thepresent invention, it is thus possible to use a simplified opticalsystem to reduce color flares. When λc does not reach the lower limit tocondition (14), color flares become striking to the eye. When the upperlimit is exceeded, color reproducibility becomes worse.

As explained above, the aforesaid condition (14) should preferably besatisfied with respect to λ1 at which (Lλ−Ld)/F_(min)=0.05 mm. Inconsideration of the fact that the obtained electronic image is oftenenlarged for observation, however, condition (14) should more preferablybe satisfied with respect to λ1 at which (Lλ−Ld)/F_(min)=0.04 mm. Evenmore preferably, condition (14) should be satisfied with respect to λ1at which (Lλ−Ld)/F_(min)=0.03 mm.

It is noted that to satisfy the aforesaid condition (14), the spectraltransmittance characteristics of the wavelength correction filter 3 maybe controlled. Alternatively, the overall spectral transmittancecharacteristics of the image pickup optical system may be controlled byproviding thereon with a wavelength correction coating, etc.

While the axial chromatic aberrations have so far been explained, it isunderstood that the same also holds for chromatic aberrations ofmagnification. FIG. 24 is an aberration diagram for the amount ofchromatic aberrations of magnification for a wavelength λ with respectto d-line. In FIG. 24, the amount Sλ of transverse chromatic aberrationof magnification for the wavelength λwith respect to d-line at an imageheight ratio of 0.9 with respect to the maximum image height IH isindicated by an arrow. FIG. 25 is illustrative of the state of chromaticaberrations at the image height ratio of 0.9 on the image plane asillustrated on the paraxial image plane 104 of FIG. 21. In this state,color flares occur.

Here let λ2 represent a wavelength at which the following condition (15)is satisfied:|Sλ|=0.025 mm  (15)where Sλ is the amount of transverse chromatic aberration ofmagnification for an arbitrary wavelength λ with respect to d-line(587.56 nm) at an image height ratio of 0.9 with respect to the maximumimage height, and |Sλ| is the amount of a displacement on the paraxialimage plane 104. While λ2 exists on a shorter wavelength side withrespect to d-line, it is preferable that the following condition (16)should be satisfied with respect to a wavelength λc whose transmittanceis a half-value of d-line transmittance.λ2≦λc≦d-line (587.56 nm)  (16)

When the wavelength λc does not reach the lower limit to condition (16),color flares become striking to the eye. When the upper limit isexceeded, color reproducibility becomes worse.

As explained above, the aforesaid condition (16) should preferably besatisfied with respect to λ2 at which |Sλ|=0.025 mm. In consideration ofthe fact that the obtained electronic image is often enlarged forobservation, however, condition (16) should more preferably be satisfiedwith respect to λ2 at which |Sλ|=0.02 mm. Even more preferably,condition (16) should be satisfied with respect to λ2 at which|Sλ|=0.015 mm.

Thus, the image pickup optical system should have such a spectraltransmittance as satisfying the aforesaid condition (14) and theaforesaid condition (16) at the same time. With this image pickupoptical system, it is possible to reduce color flares both on and offthe optical axis.

The sensitivity of the human eyes to a shorter wavelength side of thevisible light range is low, and so a visible ray close to theultraviolet ray range is hardly sensible to the human eyes. Unlike thesensitivity of the human eyes, on the other hand, an image pickup deviceenables even a light ray in the visible ray range close to theultraviolet ray range to be reproduced at a level sensible to the humaneyes. Thus, the reproducibility of light in a range close to theultraviolet ray range should be lowered, while the quantity of light ina range remarkably perceptible to the human eyes should be ensured.

In order to decrease the quantity of light on the side wavelengthsshorter than 390 nm hardly perceptible to the human eyes and ensure thequantity of light on the side wavelengths longer than 430 nm easilyperceptible to the human eyes, it is preferable to use an image pickupoptical system in which the following condition (17) is satisfied withrespect to a wavelength λc whose transmittance is a half-value of d-linetransmittance.390 nm≦λc−440 nm  (17)

In this case, even when the axial chromatic aberrations of the imagepickup optical system itself become worse, there is little or noinfluence on the image to be reproduced.

Here let F_(min) represent the minimum F-number of the image pickupoptical system, and Lλ represent the absolute value of the amount ofspherical aberration for a marginal ray having an arbitrary wavelength λand Ld represent the absolute value of the amount of sphericalaberration for a marginal ray at d-line (587.56 nm) when the F-number isF_(min), and λ1 represent a wavelength capable of satisfying thefollowing condition (13):(Lλ−Ld)/F_(min)=0.05 mm  (13)For the image pickup optical system, it is then preferable to satisfythe following condition (18) with respect to the wavelength λ1.390 nm≦λ1≦430 nm  (18)

When the wavelength λ1 becomes less than the lower limit to theaforesaid condition (18), it is impossible to cut down the cost of theoptical system because precision must be given thereto. At greater thanthe upper limit, it is impossible to achieve perfect elimination ofcolor flares.

When the lower limit to the aforesaid condition (17) is not reached,color flares become striking to the eye on the shorter wavelength side.Exceeding the upper limit to condition (17) makes color reproducibilityworse.

As explained above, the aforesaid condition (18) should preferably besatisfied with respect to λ1 at which (Lλ−Ld)/F_(min)=0.05 mm. Inconsideration of the fact that the obtained electronic image is oftenenlarged for observation, however, condition (18) should more preferablybe satisfied with respect to λ1 at which (Lλ−Ld)/F_(min)=0.04 mm. Evenmore preferably, condition (18) should be satisfied with respect to λ1at which (Lλ−Ld)/F_(min)=0.03 mm.

For chromatic aberrations of magnification, too, the image pickupoptical system according to the second aspect of the present inventionshould also satisfy the aforesaid condition (17). Here let Sλ representthe amount of transverse chromatic aberration of magnification for awavelength λ with respect to d-line (587.56 nm) at an image height ratioof 0.9 with respect to the maximum image height, and λ2 represent awavelength capable of the following condition (15):|Sλ|=0.025 mm  (15)For this optical system, it is further preferable that the followingcondition (19) is satisfied with respect to λ2.390 nm≦λ2<430 nm  (19)

When the wavelength λ2 becomes less than the lower limit to theaforesaid condition (19), it is impossible to cut down the cost of theoptical system because precision must be given thereto. At greater thanthe upper limit, it is impossible to achieve perfect elimination ofcolor flares.

As explained above, the aforesaid condition (19) should preferably besatisfied with respect to λ2 at which |Sλ|=0.025 mm. In consideration ofthe fact that the obtained electronic image is often enlarged forobservation, however, condition (18) should more preferably be satisfiedwith respect to λ2 at which |Sλ|=0.02 mm. Even more preferably,condition (18) should be satisfied with respect to λ2 at which|Sλ|=0.015 mm.

The aforesaid conditions (17), (18) and (19) should preferably besatisfied at the same time, because it is possible to reduce colorflares both on and off the optical axis.

The image pickup optical system according to the second aspect of thepresent invention is an image pickup optical system designed to form theimage of a subject on the electronic image pickup device. Here again,let F_(min) represent the minimum F-number of the image pickup opticalsystem, Lλ represent the absolute value of the amount of sphericalaberration for a marginal ray having an arbitrary wavelength λ and Ldrepresent the absolute value of the amount of spherical aberration for amarginal ray at d-line (587.56 nm) when the F-number is F_(min) and λ1represent a wavelength capable of satisfying the following condition(13):(Lλ−Ld)/F _(min)=0.05 mm  (13)For the image pickup optical system it is then preferable to satisfy thefollowing condition (20) with respect to the wavelength λ1.350 nm≦λ1≦550 nm  (20)Further, let τ(λ1) represent the transmittance ratio of the image pickupoptical system at the wavelength λ1 with respect to d-linetransmittance, and τ(λ1+30) represent the transmittance ratio of theimage pickup optical system at a wavelength λ1+30 nm with respect tod-line transmittance. Then, the image pickup optical system shouldpreferably satisfy the following conditions (21) and (22):τ(λ1)≦10%  (21)τ(λ1+30)≧50%  (22)

It is thus possible to reduce the wavelength responsible for colorflares on the shorter wavelength side where axial chromatic aberrationsoccur and to ensure light quantity with little or no influence ofchromatic aberrations in the wavelength range perceptible to the humaneyes. In other words, it is possible to achieve a compact image pickupoptical system that can make a reasonable tradeoff between colorreproducibility and rendering capability.

When the wavelength λ1 becomes less than the lower limit to theaforesaid condition (20), it is impossible to cut down the cost of theoptical system because precision must be given thereto. At greater thanthe upper limit, it is impossible to achieve perfect elimination ofcolor flares.

When the wavelength λ1 transmittance becomes greater than 10%, colorflares become striking to the eye. When the wavelength λ1+30 nmtransmittance becomes less than 50%, color reproducibility becomesworse.

As explained above, the aforesaid condition (20) should preferably besatisfied with respect to λ1 at which (Lλ−Ld)/F_(min)=0.05 mm. Inconsideration of the fact that the obtained electronic image is oftenenlarged for observation, however, the aforesaid conditions (20), (21)and (22) should more preferably be satisfied with respect to λ1 at which(Lλ−Ld)/F_(min)=0.04 mm. Even more preferably, conditions (20), (21) and(22) should be satisfied with respect to λ1 at which(Lλ−Ld)/F_(min)=0.03 mm.

For chromatic aberrations of magnification, too, the image pickupoptical system according to the second aspect of the present inventionshould also satisfy requirements similar to those for axial chromaticaberrations. Here let Sk represent the amount of transverse chromaticaberration of magnification for a wavelength λ with respect to d-line(587.56 nm) at an image height ratio of 0.9 with respect to the maximumimage height, and λ2 represent a wavelength capable of the followingcondition (15):|Sλ|=0.025 mm  (15)This optical system should satisfy the following condition (23) withrespect to λ2.350 nm≦λ2≦550 nm  (23)Further, let τ(λ2) represent the transmittance ratio of the image pickupoptical system at the wavelength λ2 with respect to d-linetransmittance, and τ(λ2+30) represent the transmittance ratio of theimage pickup optical system at a wavelength λ2+30 nm with respect tod-line transmittance. Then, the image pickup optical system shouldpreferably satisfy the following conditions (24) and (25):τ(λ2)≦10%  (24)τ(λ2+30)≧50%  (25)

It is thus possible to reduce the wavelength responsible for colorflares on the shorter wavelength side where axial chromatic aberrationsoccur and to ensure light quantity with little or no influence ofchromatic aberrations in the wavelength range perceptible to the humaneyes. In other words, it is possible to achieve a compact image pickupoptical system that can make a reasonable tradeoff between colorreproducibility and rendering capability.

When the wavelength λ2 becomes less than the lower limit to theaforesaid condition (23), it is impossible to cut down the cost of theoptical system because precision must be given thereto. At greater thanthe upper limit, it is impossible to achieve perfect elimination ofcolor flares.

When the wavelength λ2 transmittance becomes greater than 10%, colorflares become striking to the eye. When the wavelength λ2+30 nmtransmittance becomes less than 50%, color reproducibility becomesworse.

As explained above, the aforesaid conditions (23), (24) and (25) shouldpreferably be satisfied with respect to λ2 at which |Sλ|=0.025 mm. Inconsideration of the fact that the obtained electronic image is oftenenlarged for observation, however, the aforesaid conditions (23), (24)and (25) should more preferably be satisfied with respect to λ2 at which|Sλ|=0.02 mm. Even more preferably, conditions (23), (24) and (25)should be satisfied with respect to λ2 at which |Sλ|=0.015 mm.

If the aforesaid conditions (20), (21), (22), (23), (24) and (25) aresatisfied at the same time, it is then possible to achieve an imagepickup optical system with more reduced color flares both on and off theoptical axis.

The image pickup optical system according to the second aspect of thepresent invention is an image pickup optical system designed to form theimage of a subject on the electronic image pickup device. Here again,let F_(min) represent the minimum F-number of the image pickup opticalsystem, and Lh represent the absolute value of the amount of sphericalaberration for an h-line (404.7 nm) marginal ray, Lg represent theabsolute value of the amount of spherical aberration for a g-line (435.8nm) marginal ray and Ld represent, the absolute value of the amount ofspherical aberrations a d-line (587.56 nm) marginal ray when theF-number is F_(min), τh represent the h-line transmittance of the imagepickup optical system with respect to d-line, and τg is the g-linetransmittance with respect to d-line. Then, the image pickup opticalsystem should preferably satisfy the following condition (26) as well asthe following condition (27) providing that a wavelength λc whosetransmittance is a half-value of d-line transmittance should existbetween g-line and h-line.(Lg−Ld)/F _(min) ×τh≦(Lg−Ld)/F _(min) ×τg  (26)h-line (404.7 nm)<λc<g-line (435.8 nm)  (27)

On the left side of the aforesaid condition (26), the magnitude ofh-line “color running” with respect to d-line “color running” in thevicinity of the optical axis is multiplied by the h-line transmittance,and on the right side the magnitude of g-line “color running” withrespect to d-line “color running” in the vicinity of the optical axis ismultiplied by the g-line transmittance.

In general, an image pickup optical system using light in the visiblerange as a light source is designed in such a way as to eliminateaberrations in the vicinity of d-line, and so the h-line is greater inthe magnitude of “color running” than the g-line. Thus, if the aforesaidcondition (26) is satisfied or the h-line transmittance is decreased andthe g-line transmittance is increased, it is then possible to reducecolor flares depending on the h-line.

If the aforesaid condition (27) is satisfied or the wavelength λc whosetransmittance is a half-value of g-line transmittance is allowed toexist between the g-line and the h-line, it is then possible to ensurelight quantity for the g-line and color reproducibility.

For chromatic aberrations of magnification, too, the image pickupoptical system according to the second aspect of the present inventionshould also satisfy requirements similar to those for axial chromaticaberrations. Here let Sh represent the amount of transverse chromaticaberration of magnification for h-line (404.7 nm) with respect to d-line(587.56 nm) at an image height ratio of 0.9 with respect to the maximumimage height, Sg represent the amount of transverse chromatic aberrationof magnification for g-line (435.8 nm) with respect to d-line (587.56nm) at an image height ratio of 0.9 with respect to the maximum-imageheight, τh represent the h-line transmittance ratio of the image pickupoptical system with respect to d-line and τg represent the g-linetransmittance ratio with respect to d-line. Then, the image pickupoptical system should preferably satisfy the following condition (28)|Sh|×τh≦|Sg|×τg  (28)as well as the aforesaid condition (27) providing that the wavelength λcwhose transmittance is a half-value of d-line transmittance should existbetween the g-line and the h-line.

Oh the left side of the aforesaid condition (28), the h-line color shiftwith respect to d-line due to chromatic aberrations of magnification ismultiplied by the h-line transmittance, and on the right side the g-linecolor shift with respect to d-line due to chromatic aberrations ofmagnification is multiplied by the g-line transmittance.

As mentioned above, the h-line is greater in the magnitude of “colorrunning” than the g-line. Thus, if the aforesaid condition (28) issatisfied or the h-line transmittance is decreased and the g-linetransmittance is increased, it is then possible to reduce color flaresdepending on the h-line.

If the aforesaid condition (27) is satisfied or the wavelength λc whosetransmittance is a half-value of g-line transmittance is allowed toexist between the g-line and the h-line, it is then possible to ensurelight quantity for the g-line and color reproducibility.

The limits to the wavelengths used, as defined by the aforesaidconditions, may be primarily determined by the vitreous materials usedfor the optical elements. However, it is acceptable to locate in theimage pickup optical system a filter acting as a wavelength correctionfilter that makes primary correction for wavelengths. Alternatively,lenses may be each provided on its surface with a coating for makingcorrection for wavelengths.

The image pickup optical system can be fabricated with ease by applyingcoating films for correcting wavelengths on planes.

The number of optical elements can be reduced by locating a low-passfilter in the image pickup optical system and applying awavelength-correcting coating on at least one surface of the low-passfilter.

The number of optical elements can also be reduced by locating in theimage pickup optical system an infrared cutoff filter for reducinginfrared light components and applying a wavelength-correcting coatingon at least one surface of the infrared cutoff filter.

If coating is carried out in such a way that the wavelength whosetransmittance is a half-value of d-line transmittance exists betweeng-line and h-line, and between 600 nm and 700 nm, it is then possible todispense with such an infrared cutoff filter, again resulting in adecrease in the number of optical elements.

When correction of wavelengths is carried out by an optical pathsplitter means located in the optical path of the image pickup opticalsystem, it is preferable to locate the wavelength-correcting element onan optical path alone, which has an image pickup area whose g-linesensitivity is 30% or more of e-line sensitivity and is positioned onthe side of the image pickup device.

The fact that the sensitivity to g-line is 30% or more of thesensitivity to e-line means that color flares are likely to occur atshort wavelengths. If wavelengths responsible for chromatic aberrationsare reduced by the aforesaid wavelength-correcting element, it is thenpossible to ensure the desired light quantity for another optical pathwithout recourse to the aforesaid wavelength-correcting element, becausethe influence of short wavelengths on another optical path is limited.

For instance, if one of the optical paths obtained by the optical pathsplitter means is used as an observation optical path guided to the eyeof the observer, it is unnecessary to locate any wavelength-correctingelement because the sensitivity of the human eyes to short wavelengthsis inherently low.

For a so-called multi-plate image pickup system comprising image pickupelements having different spectral sensitivity characteristics, whichare separately mounted on some of optical paths obtained by the opticalpath splitter means, it is unnecessary to locate the aforesaidwavelength-correcting element on an optical path whose sensitivity toshort wavelengths is low and which is positioned on the side of theimage pickup devices.

According to the second aspect of the present invention, there isprovided an image pickup optical system for forming a subject image onan electronic image pickup device, characterized by having an opticalpath with a light quantity control element being located therein so asto carry out wavelength correction in such a way that the sensitivity ofsaid element to a wavelength between g-line and h-line is a half-valueof e-line transmittance.

According to this embodiment of the second aspect, it is possible toreduce the number of optical elements because of no need of providingany additional wavelength-correcting means.

More specifically, the action of correcting wavelengths can be obtainedby applying coating on the control element or mixing an absorption dyewith the control element.

In this embodiment, too, it is preferable to satisfy any one of theconditions mentioned so far herein. It is also understood that theseconditions may be used in combination of two or more.

For the image pickup optical system according to the second aspect ofthe present invention, it is preferable that the optical path takingpart in the determination of the focal length therein is constructed ofan optical element making use of a refraction phenomenon alone, becauseits construction can be simplified.

According to the image pickup system of the second aspect of the presentinvention, it is acceptable to locate at the back focal position of theimage pickup optical system an electronic image pickup device havingthree or more different spectral sensitivity characteristics so as toobtain a color image.

If at least one of electronic image pickup devices having three or moredifferent spectral sensitivity characteristics is provided with aso-called complementary type mosaic filter which has two high peakwavelengths, between which there is a wavelength having a 50% or lesssensitivity to both peak wavelengths, then the sensitivity to shortwavelengths becomes higher than required. This is effective for eachembodiment of the second aspect of the present invention.

The third aspect of the present invention is now explained.

The purport of the third aspect of the invention is to make correctionfor chromatic aberrations for h-line as is the case with chromaticaberrations for d-line. Even when the h-line of the subject isreproduced with a blue wavelength easily perceptible to the human eyes,color flares with blue becoming striking remarkably to the eyes can beeliminated by superposing another wavelength on the blue wavelength.

According to the third aspect of the present invention, there isprovided an electronic image pickup system comprising an electronicimage pickup device including a plurality of pixels having three or morespectral characteristics to obtain a color image and an image pickupoptical system for forming a subject image on the image pickup surfaceof the electronic image pickup device, characterized in that:

said image pickup optical system satisfies the following conditions (31)and (32):(Lh−Ld)/F _(min)≦0.07 mm  (31)|Sh|≦0.04 mm  (32)where F_(min) is the minimum F-number, Lh is the absolute value of theamount of spherical aberrations for an h-line (404.7 nm) marginal rayand Ld is the absolute value of the amount of spherical aberrations fora d-line (587.56 nm) when said optical system is focused on an infiniteobject point with F-number=F_(min), and Sh is the amount of transversechromatic aberration of magnification for h-line with respect to d-lineat an image height ratio of 0.9, 0.7 and 0.5 with respect to the maximumimage height.

According to the third aspect of the present invention, there is alsoprovided an electronic image pickup system comprising an electronicimage pickup device including a plurality of pixels having three or morespectral characteristics to obtain a color image and an image pickupoptical system for forming a subject image on the image pickup surfaceof the electronic image pickup device, characterized in that:

said image pickup optical system satisfies the following conditions (33)and (34):(Lh−Ld)/F _(min)≦6P  (33)|Sh|≦5P  (34)where P is the minimum pixel pitch, F_(min) is the minimum F-number, Lhis the absolute value of the amount of spherical aberrations for anh-line (404.7 nm) marginal ray and Ld is the absolute value of theamount of spherical aberrations for a d-line (587.56 nm) when saidoptical system is focused on an infinite object point withF-number=F_(min), and Sh is the amount of transverse chromaticaberration of magnification for h-line with respect to d-line at animage height ratio of 0.9, 0.7 and 0.5 with respect to the maximum imageheight.

In addition, the electronic image pickup system according to the thirdaspect of the present invention should preferably satisfy the followingconditions (35) and (36):(Lh−Ld)/F _(min)≧0.5P  (35)|Sh|≧0.03P  (36)

According to the first embodiment of the fourth aspect of the presentinvention, there is provided an image pickup system characterized bycomprising, at least:

an electronic image pickup device satisfying the following condition(41) and including a complementary filter comprising at least four colorfilter elements,

an image pickup optical system having spectral characteristics given bythe following conditions (42) and (43) and provided for guiding a lightbeam from the object side of the image pickup system to the electronicimage pickup device, and

a controller for carrying out signal processing and image processing onthe basis of an output from the electronic image pickup device:1.0×10⁻⁴ <p/d<6.0×10⁻⁴  (41)8×T ₇₀₀ <T ₆₀₀  (42)T₄₀₀<T₆₀₀  (43)where d is the diagonal length of an effective image pickup area of theimage pickup device, p is the center separation between horizontalpixels, T₄₀₀ is a 400-nm transmittance, T₆₀₀ is a 600-nm transmittanceand T₇₀₀ is a 700-nm transmittance.

The action and effect of the first embodiment of the image pickup systemaccording to the second aspect of the present invention are nowexplained.

Condition (41) gives a definition of the number of pixels in thehorizontal direction, which is required to obtain high image quality.The resolving power of the human eye is said to be high in thehorizontal direction in particular. When the upper limit of 6.0×10⁻⁴ incondition (41) is exceeded, rough images of poor image quality areobtained, and there is little or no need of obtaining the effect (to bedescribed later) due to the use of other constituting elements in thefourth aspect of the present invention. When the lower limit of 1.0×10⁻⁴in condition (41) is not reached, pixel size becomes too small to ensuresufficient light quantity, and the effect on image quality improvementsis unachievable because of the influence of diffraction. In addition,the whole size of the image pickup device becomes large, resulting in anincrease in the size of the phototaking optical system, which iscontrary to significant size reductions. In consideration of cost, toosmall a p/d value is not preferable because the whole size of an imagepickup device such as a CCD has a great influence on its cost.

By use of a complementary color filter, it is possible to ensure lightquantity per unit area. A four-color filter comprises magenta (M), cyan(C), yellow (Y_(e)) and green (G), of which cyan (C), yellow (Ye) andgreen (G) have sensitivity to green light (light in the wavelength rangeof about 500 nm to about 550 nm) that is a significant determinant forimage resolution; at least 75% of effective pixels have a largeinfluence on image resolution. With this complementary color filter, itis thus possible to increase the number of pixels, as defined bycondition (41).

Condition (42) gives a definition of infrared cutoff. By satisfying thiscondition, it is inevitably possible to reduce the 700-nm transmittancedown to 12.5% or less and so achieve sufficient infrared cutoff effects.A deviation from the range defined by condition (42) causes light in theinfrared range—which cannot be perceived by the human eyes as colors—tohave a large influence on red development, and causes ill-balancedexposure, resulting in a failure in achieving preferable colorreproduction.

Condition (43) gives a definition of the influence of a shorterwavelength side on red development by the complementary color filter. Incolor conversion by the complementary filter to R, G and B, R signals(for red development) are produced upon incidence of light in the bluewavelength range (of about 400 nm to about 430 nm in FIG. 70). Whenthere is a deviation from the upper limit to condition (43), the inputof wavelengths shorter than the red wavelength has a large influence onthe strength of R signals, making color reproduction worse. Especiallyin the case of a phototaking optical system wherein large chromaticaberrations occur on the side of wavelengths shorter than a wavelengthin the primary visible range, the spread of an originally unobtrusivespot on the shorter wavelength side (the so-called flares produced bychromatic spherical aberrations, coma, chromatic aberrations ofmagnification, etc.) develops striking red, resulting in image qualitydeterioration.

By satisfying conditions (42) and (43) with the use of the complementarycolor filter, it is possible to achieve satisfactory color reproduction.Even with a phototaking optical system with increased chromaticaberrations, the flares on the shorter wavelength side are sufficientlyweaker as compared with images in the visible range, and so aresubstantially unlikely to have an influence on image quality, inconsideration of the sensitivity of the human eyes.

With such a phototaking optical system, it is possible to construct atotally preferable phototaking system, because by producing chromaticaberrations on the side of wavelengths shorter than those in the primaryvisible range, it is possible to make the optical system compact,provide easy fabrication of the optical system, decrease the number oflenses, decrease the F-number of the optical system, make the fieldangle of the optical system larger than the standard (in return for theproduction of off-axis chromatic aberrations) or smaller than thestandard (in return for the production of axial chromatic aberrations),and increase zoom ratios in the case of a zoom lens system.

It is noted that the controller may be used for the conversion ofcomplementary colors to R, G and B, gamma correction, etc.

It is not always necessary to construct the phototaking optical system,electronic image pickup device and controller in a monolithic form. Forinstance, the image pickup optical system may be designed to bedetachable from equipment including the electronic image pickup device,and it is acceptable to use a plurality of image pickup optical systems.

It is desired that p be in the range of 1.8 μm to 3.9 μm inclusive. Atgreater than the upper limit of 3.9 μm, the whole area of the electronicimage pickup device increases, resulting in cost increases. At less thanthe lower limit of 1.8 μm, it is difficult to impart sufficient lightquantity to each pixel of the image pickup device. More preferably, pshould be in the range of 2.1 μm to 3.5 μm inclusive. At greater thanthe upper limit of 3.5 μm, the whole area of the electronic image pickupdevice becomes large, resulting in cost increases. At less than thelower limit of 2.1 μm, it is difficult to set up, with simpleconstruction and at low costs, a phototaking optical system havingchromatic aberrations acceptable to the fourth aspect of the presentinvention. If p is in the range of 2.1 μm to 3.2 μm inclusive, thebalance of the image pickup device is then more improved.

According to the second embodiment of the fourth aspect of the presentinvention, there is provided an image pickup system comprising, atleast:

a phototaking optical system,

an electronic image pickup device having a complementary color filtercomprising at least four color filter elements,

said electronic optical system satisfying the following condition (41),and

a controller for implementing signal process and image processing on thebasis of an output from the electronic image pickup device, and

a spectral strength curve for output signals that are produced from theelectronic image pickup device upon incidence of light from thephototaking optical system thereon and photoelectric conversion of thelight and correspond to at least one color filter (a curve delineated bythe strength of an output signal at each wavelength when light isincident from a light source D₆₅ on the phototaking optical system)satisfies the following condition (44):1.0×10⁻⁴ <p/d<6.0×10⁻⁴  (41)0.45<(S ₆₀₀−S₆₅₀)/Sp<0.85  (44)where d is the diagonal length of an effective image pickup area, p isthe center separation between horizontal pixels, Sp is the spectralstrength peak, S₆₀₀ is the strength of 600 nm and S₆₅₀ is the strengthof 650 nm.

Condition (41) and the complementary color filter are the same as in thecase of the first image pickup system according to the fourth aspect ofthe present invention.

Condition (44) gives a definition of infrared cutoff and the so-calledred signal strength. Within the range defined by this condition, it ispossible to obtain red signals of sufficient strength and relativelyreduce the influence of the shorter wavelength side on the reddevelopment signals calculated at the controller. It is thus possible toachieve substantially satisfactory color reproduction while the effectof the complementary color filter is available. Falling short of thelower limit of 0.45 in condition (44) is not preferable, because it isimpossible to obtain red signals of sufficient strength. Exceeding theupper limit of 0.85 in condition (44) is not preferable, because it isdifficult to make color or infrared cutoff filters or fabricate byevaporation a thin-film coating having an infrared cutoff function,resulting in cost increases or a productivity drop due to complicateddesigns.

According to the third embodiment of the fourth aspect of the presentinvention, the first or second image pickup system is furthercharacterized in that the electronic image pickup device comprises acomplementary color filter having at least four color filter elements inwhich:

a first color filter G has a peak at a wavelength Gp

a second color filter Ye has a peak at a wavelength Yp,

a third color filter C has a peak at a wavelength Cp, and

a fourth color filter M has peaks at wavelengths M_(p1) and M_(p2),provided that510 nm<Gp<540 nm  (45-1)5 nm<Yp−Gp<35 nm  (45-2)−100 nm<Cp−Gp<−5 nm  (45-3)430 nm<M_(p1)<480 nm  (45-4)580 nm<M_(p2)<640 nm  (45-5)

The action and effect of the third image pickup system according to thefourth aspect of the present invention are now explained. By satisfyingconditions (45-1) to (45-5), it is possible to achieve satisfactoryimage reproduction and allow G, Ye and C to have sufficient sensitivityto green (light in the wavelength range of about 500 nm to about 550 nm)that is a significant determinant for image resolution, therebyobtaining image resolution consistent with the large number of pixels.

According to the fourth embodiment of the fourth aspect of the presentinvention, the third image pickup system is further characterized inthat the electronic image pickup device comprises a complementary colorfilter comprising at least four color filter elements, three colorfilter elements of which have a strength of 80% or greater at 530-nmwavelength with respect to their spectral strength peaks and one ofwhich has a strength of 25% or greater at 530-nm wavelength with respectits spectral strength peak.

The action and effect of the fourth image pickup system are nowexplained. According to the construction of this image pickup system, itis possible to fetch information having an influence on image resolutionfrom all the color filter elements.

According to the fifth embodiment of the fourth aspect of the presentinvention, any one of the first through fourth image pickup systems isfurther characterized in that the electronic image pickup devicecomprises a complementary color filter assembly comprising at least fourcolor filters which are positioned in such a mosaic manner thatsubstantially the same number of filter elements are used for each colorand adjacent pixels do not correspond to the same kind of color filterelements.

The action and effect of the fifth image pickup system according to thefourth aspect of the present invention are now explained. According tothe construction of this image pickup system, image quality is generallyimproved with improvements in image resolution, color reproduction andcolor resolution.

According to the sixth embodiment of the fourth aspect of the presentinvention, any one of the first through fifth image pickup systems isfurther characterized by comprising an optical element located on anobject side of the system with respect to the electronic image pickupdevice, said optical element being coated by evaporation with a thinfilm having a 600-nm transmittance of 80% or greater and a 700-nmtransmittance of 10% or less.

The action and effect of the sixth image pickup system are nowexplained. According to this construction, it is possible to achieve atlow costs an image pickup system having the combined properties of thefirst and second image pickup systems. The so-called infrared cutofffunction of cutting off light rays of 700 nm or greater may be achievedby use of an infrared cutoff filter or a combination of thin-film coatsprovided by evaporation on a plurality of lenses forming a phototakingoptical system. However, this causes a drop of 600-nm transmittance. Toensure sufficient 600-nm transmittance and sufficient red input signals,it is preferable to use a thin-film coat obtained by evaporation on onesurface, thereby achieving such characteristics as mentioned above.

According to this process, the site having a main infrared cutofffunction is so thin that it is possible to prevent the overalltransmittance from decreasing excessively and, hence, reduce the size ofthe phototaking system. In addition, the number of sites that must becontrolled with infrared cutoff in mind is so reduced that productivitysuch as yields can be improved, resulting in some considerable costreductions.

More preferably, the optical element should be coated by evaporationwith a thin film having a 600-nm transmittance of 90% or greater and a700-nm transmittance of 10% or less.

According to the seventh embodiment of the fourth aspect of the presentinvention, any one of the first through sixth image pickup systems isfurther characterized by comprising a phototaking optical system havingan area with an effective diagonal field angle of 70° or greater.

The action and effect of the seventh image pickup system are nowexplained. At an effective diagonal field angle of 70° or greater,off-axis aberrations, viz., chromatic aberrations of magnification andchromatic coma are likely to occur. According to the fourth aspect ofthe present invention, it is possible to achieve a high image-qualityphototaking system which enables colors to be reproduced with imageresolution yet without recourse to any complicated construction, i.e.,with little or no use of special optical elements or costly materials.It is understood that a zoom phototaking optical system having aneffective diagonal field angle of 70° or greater at its wide-angle end,too, is embraced in this aspect of the present invention.

According to the eighth embodiment of the fourth aspect of the presentinvention, any one of the first through sixth image pickup systems isfurther characterized by comprising a phototaking optical system havingan area with an effective diagonal field angle of 12° or less.

The action and effect of the eighth image pickup system are nowexplained. At an effective diagonal field angle of 12° or less, theproportion of a focal length difference due to wavelengths is likely tobecome large and so axial aberrations, viz., chromatic sphericalaberrations are likely to occur. According to the fourth aspect of thepresent invention, it is possible to achieve a high image-qualityphototaking system which enables colors to be reproduced with imageresolution yet without recourse to any complicated construction, i.e.,with little or no use of special optical elements or costly materials.It is understood that a zoom phototaking optical system having aneffective diagonal field angle of 12° or less at its wide-angle end,too, is embraced in this aspect of the present invention.

According to the ninth embodiment of the fourth aspect of the presentinvention, any one of the first through sixth image pickup systems isfurther characterized by comprising a phototaking optical system havingan area with an F-number of 2.8 or less.

The action and effect of the ninth image pickup system are nowexplained. A small F-number makes it possible to obtain sufficient lightintensity even when pixel size is small. At an F-number of 2.8 or less,chromatic spherical aberrations and chromatic coma are likely to occur.According to the fourth aspect of the present invention, it is possibleto achieve a high image-quality phototaking system which enables colorsto be reproduced with image resolution yet without recourse to anycomplicated construction, i.e., with little or no use of special opticalelements or costly materials. It is understood that a zoom phototakingoptical system having an F-number of 2.8 or less at its wide-angle end,too, is embraced in this aspect of the present invention.

According to the tenth embodiment of the fourth aspect of the presentinvention, any one of the first through sixth image pickup systems isfurther characterized by comprising a phototaking optical systemcomprising, in order from an object side of the phototaking opticalsystem, a positive, first lens group, a negative, second lens group thatis movable during zooming and a lens group having a focusing function,said lens group being located on an image side of the phototakingoptical system with respect to the second negative lens group.

The action and effect of the tenth image pickup system are nowexplained. An axial light beam incident from the object side of thesystem on the positive, first lens group enters the negative, secondlens group while it is converged. In other words, the diameter of thesecond lens group can be decreased. This effect in turn enables thepower of the second lens group to be so increased that the zoom ratiocan be easily increased with a decrease in the F-number. Accordingly,the power of the first lens group, too, can become strong and, hence,higher-order chromatic aberrations of magnification are likely to occur.An increased zoom ratio makes higher-order chromatic aberrations ofmagnification likely to occur with zooming. This influence becomesprominent as the number of pixels increases as defined by condition(41). Referring here to axial chromatic aberrations, it is impossible tomake perfect correction for the chromatic aberrations due to secondaryspectra on the telephoto side in particular. Referring to aberrationsdue to reference wavelength which are not the so-called chromaticaberrations, they can be well corrected within each group or betweengroups with a relatively reduced number of lenses and an inexpensivematerial. If this image pickup system has such properties as explainedwith reference to the first and second image pickup systems, it is thenpossible to obtain substantially satisfactory image quality withoutrecourse to any complicated or large construction or any special opticalelements or costly materials, even when relatively large aberrations areproduced on the short wavelength side in particular. To locate the lensgroup having a focusing function on the image side of the image pickupoptical system with respect to the second lens group is favorable forensuring a focusing space. This is particularly advantageous for aphototaking optical system compatible with an electronic image pickupdevice with an exit pupil set at a remote point, because imagedeterioration due to an object point distance variation can be reduced.

According to the eleventh embodiment of the fourth aspect of the presentinvention, the tenth image pickup system is further characterized bycomprising a phototaking optical system comprising, in order from anobject side of the phototaking optical system, a positive, first lensgroup, a negative, second lens group that is movable during zooming, apositive, third lens group and a fourth lens group that is movableduring zooming and has a focusing function.

The action and effect of the eleventh image pickup system are nowexplained. By using the positive, third lens group, it is easy to makelight incident on the electronic image pickup device nearly vertical topixels, i.e., locate the exit pupil at a remote point. Preferably, anaperture stop should be located between the second lens group and thethird lens group, so that the exit pupil can be set at a much remoterpoint.

According to the twelfth embodiment of the fourth aspect of the presentinvention, the eleventh image pickup system is further characterized bycomprising a phototaking optical system comprising, in order from anobject side of the phototaking optical system, a positive, first lensgroup, a negative, second lens group that is movable during zooming, apositive, third lens group that is movable during zooming and apositive, fourth lens group that is movable during zooming and has afocusing function.

The action and effect of the twelfth image pickup system are nowexplained. The positive, third lens group, because of being designed tobe movable, can share the zooming action of the second lens group, sothat zoom ratio improvements can be easily achieved with an F-numberdecrease. By giving positive power to the fourth lens group, the fourthlens group can share the ability of the third lens group to set the exitpupil at a remote point, so that the zooming function of the third lensgroup can be enhanced.

According to the thirteenth embodiment of the fourth aspect of thepresent invention, the eleventh image pickup system is furthercharacterized by comprising a phototaking optical system comprising, inorder from an object side of the phototaking optical system, a positive,first lens group, a negative, second lens group that is movable duringzooming, a generally positive, third lens group that is located on animage side of the phototaking optical system with respect to the secondlens group and includes at least a positive lens and a negative lens,and a lens group that is located on an image side of the phototakingoptical system with respect to the third lens group and has positivepower and a focusing function.

The action and effect of the thirteenth image pickup system are nowexplained. The positive-negative power profile of the third lens groupmakes it possible to locate the principle point at a relatively frontpoint and the positive lens group is located on the image side, therebymaking the overall length of the image pickup system short.

According to the fourteenth embodiment of the fourth aspect of thepresent invention, the thirteenth image pickup system is furthercharacterized by comprising a phototaking optical system comprising, inorder from an object side of the phototaking optical system, a positive,first lens group, a negative, second lens group that is movable duringzooming, a generally positive, third lens group that is located on animage side of the phototaking optical system with respect to the secondlens group and includes at least a positive lens, a positive lens and anegative lens having a strong-curvature concave surface on its imageside, and a lens group that is located on an image side of thephototaking optical system with respect to the third lens group and haspositive power and a focusing function.

The action and effect of the fourteenth image pickup system are nowexplained. The layout of the positive lens, positive lens and negativelens located in this order in the third lens group, said negative lenshaving a strong-curvature concave surface on its image side, iseffective for correction of axial light beams and off-axis coma.

If the fourth lens group is started with at least a negative lens and apositive lens in order from its object side, the third and fourth lensgroups then provide together a substantially double-Gauss type layout,which makes it easy to achieve satisfactory performance even with adecreasing F-number.

By constructing the fourth lens group of one positive lens, it is alsopossible to reduce the overall length of the image pickup system(because an axial beam is almost uniformly converged in the fourth lensgroup).

According to the fifteenth embodiment of the fourth aspect of thepresent invention, the fourteenth image pickup system is furthercharacterized by comprising a phototaking optical system comprising, inorder from an object side of the phototaking optical system, a positive,first lens group, a negative, second lens group that is movable duringzooming, a generally positive, third lens group that is located on animage side of the phototaking optical system with respect to the secondlens group and includes at least a positive lens having an asphericalsurface and a cemented component consisting of a positive lens and anegative lens having a concave surface having a curvature stronger onits image side than on its object side, and a lens group that is locatedon an image side of the phototaking optical system with respect to thethird lens group and has positive power and a focusing function.

The effect and action of the fifteenth image pickup system are nowexplained. By using the aspherical surface with the positive lenslocated on the object side in the third lens group, correction ofhigher-order spherical aberrations is carried out. It is then preferableto locate the aspherical surface on the image side of the positive lensbecause it is possible to take full advantage of the aspherical surfaceby choice of lens curvature. The subsequent positive lens followed bythe negative lens having a concave surface having a curvature strongeron its image side than on its object side provides an layout effectivefor correction of axial light beams and off-axis coma. To achieve someconsiderable reduction of a factor for image deterioration due to apossible decentration between the positive lens and the negative lens,these lenses are cemented together.

If the fourth lens group is started with at least a negative lens and apositive lens in order from its object side, the third and fourth lensgroups then provide together a substantially double-Gauss type layout,which makes it easy to achieve satisfactory performance even with adecreasing F-number.

By constructing the fourth lens group of one positive lens, it is alsopossible to reduce the overall length of the image pickup system(because an axial beam is almost uniformly converged in the fourth lensgroup).

According to the sixteenth embodiment of the fourth aspect of thepresent invention, any one of the first through sixth image pickupsystems is further characterized by comprising an image pickup opticalsystem comprising, in order from an object side of the phototakingoptical system, a negative, first lens group that is movable duringzooming, a positive, second lens group that is movable during zooming,and a lens group having a focusing function, which is located at thesecond lens group or on an image side of the optical system with respectthereto.

The action and effect of the sixteenth image pickup system are nowexplained. When the negative, first lens group and positive, second lensgroup are located in order from the object side of the optical system,the diameter of the second lens group tends to become large. However,this layout is effective for lowering the height of off-axis light beamsincident on the first lens group and, hence, for a zoom lens orwide-angle zoom lens system having a relatively low magnification of upto about 3. The diameter of the first lens group, too, can be easilydecreased so that the length of the first lens group can be reduced,thereby reducing the size of the phototaking optical system duringcollapsing. To take full advantage of this effect, it is required todecrease the number of lenses forming the first lens group (thereduction in the number of lenses does not only make a contribution tolength reductions but is also effective for decreasing the diameter ofthe lens on the object side of the first lens group or the length foreach lens). When the number of lenses forming the first lens group isreduced, on the other hand, higher-order chromatic aberrations ofmagnification are likely to occur at the wide-angle end in particular.If this image pickup system has such properties as explained withreference to the first and second image pickup systems, it is thenpossible to obtain substantially satisfactory image quality withoutrecourse to any complicated or large construction or any special opticalelements or costly materials, even when relatively large aberrations areproduced on the short wavelength side in particular.

For speedy focusing, it is preferable for the second or third lens groupto have a focusing function.

According to the seventeenth embodiment of the fourth aspect of thepresent invention, the sixteenth image pickup system is furthercharacterized by comprising an image pickup optical system comprising,in order from an object side of the image pickup optical system, agenerally negative, first lens group that is movable during zooming witha negative lens located nearest to an object side thereof, a generallypositive, second lens group that is movable during zooming and includesat least a positive lens having an aspherical surface and a cementedcomponent consisting of a positive lens and a negative lens having aconcave surface having a curvature stronger on its image side than onits object side, and a lens group that is located at the second lensgroup or on an image side with respect thereto and has positive powerand a focusing function.

The action and effect of the seventeenth image pickup system are nowexplained. According to this construction, it is possible to locate theprinciple point on a front side and ensure a zooming space between thefirst lens group and the second lens group. With the aspherical surface,it is further possible to make correction for higher-order sphericalaberrations and coma in particular. With the negative lens having aconcave surface that has a strong curvature on the image side, it ispossible to make correction for aberrations for off-axis light beams inparticular. The positive lens and the subsequent negative lens having acurvature stronger on its image side than on its object side provide anlayout effective for correction of axial light beams and off-axis coma.To achieve some considerable reduction of a factor for imagedeterioration due to a possible decentration between the positive lensand the negative lens, these lenses are cemented together.

It is preferable to locate a positive single lens on the image side ofthe second lens group, said single lens being designed to remain fixedduring zooming and have a strong curvature on its image side, becausethis single lens is effective for correction of off-axis coma, etc., andthe location of the exit pupil as well. It is also preferable to locatean aperture stop between the first lens group and the second lens group,because the exit pupil can be effectively located.

According to the eighteenth embodiment of the fourth aspect of thepresent invention, the seventeenth image pickup system is furthercharacterized by comprising an image pickup optical system comprising,in order from an object side of the image pickup optical system:

a generally negative, first lens group that is movable during zoomingwith a negative lens located nearest to the object side,

a generally positive, second lens group that is movable during zoomingand includes a positive lens having an aspherical surface and a cementedcomponent consisting of a positive lens and a negative lens having astrong-curvature concave surface on an image side thereof, and

a lens group that is located at the second lens group or or on an imageside with respect thereto and has a focusing function,

said image pickup optical system satisfying the following condition(46):−βT>1.2  (46)where βT is the magnification of the second lens group at its wide-angleend.

The action and effect of the eighteenth image pickup system are nowexplained. Condition (46) is the requirement for effectively reducingthe length of each lens group. Any deviation from condition (46) makesthe power of the first lens group strong, resulting in an increase inthe number of lenses and, hence, in the length of the system.

The lens layout for each of the tenth through eighteenth image pickupsystems is designed mainly with aberrations for reference wavelength andparaxial arrangements in mind. If this lens layout is used incombination with the first or second image pickup system, it is thenpossible to obtain ever higher image quality with more simplifiedconstruction, lower-cost construction or more compact construction.

The level of chromatic aberrations is now explained more specifically.As already mentioned, the optical system is designed in such a way thatwhen focused on an infinite object point in the range of 70% of theeffective screen, the chromatic aberrations in meridian section at a400-nm wavelength are equivalent in size to four or more pixels. It isthus possible to provide an optical system of simplified construction,which makes it possible to enhance its image-formation capability in thewavelength region taking part in image formation. In this regard, anaccount is given of the limitation that the chromatic aberrations inmeridian section are equivalent in size to four or more pixels. Hereconsider the state where the image pickup system is focused on aninfinite object point (i.e., the state where the image pickup system isfocused through an autofocusing mechanism on a nearly infinite objectpoint or it is focused on a nearly infinite object point in a manualfocusing mode set on an infinite memory, or the state where the peak ofan axial PSF (point spread function) strength at d-line (587.6 nm) ismaximized with respect to an infinite object point on an optical axis.Then, the chromatic aberrations are defined by a size δ on meridiansection, which accounts for at least 1.6% of the maximum value of thePSF strength at a specific wavelength. In other words, the aforesaidlimitation means that the size δ (400) at 400-nm wavelength isequivalent to four or more pixels.

Also assume the length from the center of the image pickup surface tothe maximum effective image height to be equal to 1. Then, the range of70% of the effective screen is defined by the inside of a circle, theradius of which is 7/10 of that length.

The present invention is further characterized in that chromaticaberrations for a wavelength of 435 nm to 600 nm are equivalent to threeor less pixels in the range of 70% of the effective screen, therebyproviding an image pickup optical system wherein the change in theimage-formation capability due to wavelength is on a practicallyacceptable level.

Here let d represent the effective diagonal length of the electronicimage pickup device, and δ(400) and δ(420) stand for chromaticaberrations at 400-nm wavelength and 420-nm wavelength as found in therange of 70% of the effective screen, respectively. It is thenpreferable to satisfyδ(400)/d>2.0×10⁻³It is more preferable to satisfyδ(420)/d<1.5×10⁻³

While the chromatic aberrations for 400-nm wavelength and 420-nmwavelength have been discussed, it is understood that even when thechromatic aberrations for 400-nm wavelength are replaced by those forh-line (404.7 nm) and the chromatic aberrations for 420-nm wavelengthare replaced by those for g-line (435.8 nm), the same effects areachievable.

Referring to the chromatic aberration of magnification, it is preferablethat the distance between the peak of a d-line spot and the peak of ag-line spot is equivalent to seven or less pixels all over the effectivescreen of the electronic image pickup device. More preferably in thiscase, the distance between the d-line and the g-line should beequivalent to ten or more pixels.

Alternatively, let Δdh, Δdg and d represent the distance between thepeaks of d- and h-lines, the distance between the peaks of d- andg-lines and the effective diagonal length of the electronic image pickupdevice, respectively. It is then preferable that at least a part of thescreen satisfiesΔdh/d>6.0×10⁻³More preferably in this case, the whole screen satisfiesΔdg/d<4.5×10−3

The aspects of the present invention as mentioned above are effectivefor making correction for the “color running” found on high-contrastboundaries (e.g., edge portions of an object image) of the phototakingimage.

In summary, the present invention can provide an electronic image pickupsystem comprising:

a phototaking optical system on which a light beam from an object isincident,

a color filter for splitting a light beam passing through thephototaking optical system into a plurality of colors,

an electronic image pickup device for sensing a light beam upon passingthrough the color filter, and

a color running correction means for reducing a color running thatoccurs at a brightness boundary in an output image from an object imagesensed by the electronic image pickup device and is included in therange defined by0.25≦x≦0.650.465x−0.076≦y≦0.25as represented in terms of x-y chromaticity coordinates.

The aforesaid range corresponds to a hatched region on a well-known x-ychromaticity diagram as shown in FIG. 83 or, in color parlance,corresponds to reddish purple or the like.

The color in this range is a color component perceived by the observeras color flares, as already explained. By making satisfactory correctionfor this color with the constructions explained above, it is possible toobtain satisfactory images.

If the aforesaid “color running” correction mechanism is used to reducedown to 1% or less an output included in the range defined by0.25≦x≦0.650.465x−0.076≦y≦0.25as represented in terms of x-y chromaticity coordinates, provided thatthe upper limit to a dynamic range is given by white.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrative of the first embodiment of thedigital camera according to the first aspect of the invention.

FIG. 2 is a schematic illustrative of the filter arrangement of aprimary colors filter.

FIG. 3 is a schematic illustrative of the filter arrangement of acomplementary colors filter.

FIG. 4 is a diagram illustrative of the wavelength characteristics ofFIG. 2.

FIG. 5 is a diagram illustrative of the wavelength characteristics ofFIG. 3.

FIG. 6 is a schematic illustrative of another embodiment of the digitalcamera according to the invention.

FIG. 7 is a schematic illustrative of yet another embodiment of thedigital camera according to the invention.

FIG. 8 is a diagram illustrative of one example of the characteristicsof the primary colors filter.

FIG. 9 is a diagram illustrative of one example of the characteristicsof the complementary colors filter.

FIG. 10 is a diagram illustrative of the characteristics of the filterused to obtain the characteristics of FIG. 9 by its superposition on thefilter having the characteristics of FIG. 5.

FIG. 11 is a diagram illustrative of one example of the transmittancecharacteristics of an image pickup lens.

FIG. 12 is a schematic illustrative of the embodiment of the inventionwherein the transmittance control filter is located on the object sideof the system with respect to the image pickup device.

FIG. 13 is a diagram illustrative of one example of the characteristicsof the antireflection coating.

FIG. 14 is a schematic illustrative of another embodiment of the digitalcamera according to the first aspect of the invention.

FIG. 15 is a sectional representation of Example A including its opticalaxis.

FIG. 16 is a sectional representation of Example B including its opticalaxis.

FIG. 17 is a sectional representation of Example C including its opticalaxis.

FIG. 18 is a sectional representation at the wide-angle end of Example Dincluding its optical axis.

FIG. 19 is a sectional representation at the wide-angle end of Example Eincluding its optical axis.

FIG. 20 is a sectional representation at the wide-angle end of Example Fincluding its optical axis.

FIG. 21 is a conceptual representation of the image pickup opticalsystem according to the second aspect of the invention.

FIG. 22 is a spherical aberration diagram for the image pickup opticalsystem of FIG. 21.

FIG. 23 is illustrative of the amount of a focal position displacementat the maximum height of incident ray when the image pickup opticalsystem of FIG. 21 is viewed in section of the back focal point.

FIG. 24 is an aberration diagram illustrative of chromatic aberration ofmagnification of the image pickup optical system for a wavelength λ withrespect to d-line.

FIG. 25 is illustrative of how chromatic aberrations of the image pickupoptical system of FIG. 21 are seen at the image height ratio of 0.9 onthe image plane.

FIG. 26 is a schematic representation of a so-called digital camera thatis one embodiment of the electronic image pickup system according to thesecond aspect of the invention.

FIG. 27 is a schematic representation of a two-dimensional areaphotometric sensor used with this electronic image pickup system.

FIG. 28 is illustrative of how a high-contrast subject is phototaken ina room with a clear sky in the background.

FIG. 29 is an enlarged view of a part of the image pickup surface, whichis illustrative of one exemplary luminance difference with respect tocorrect exposure for each pixel.

FIG. 30 is illustrative of the state of the two-dimensional areaphotometric sensor used with this electronic image pickup system.

FIG. 31 is a schematic illustrative of an electronic image pickup devicewhich is provided on its image pickup surface with a plurality ofphotometric areas as pixels, each provided with an ND filter as asensitivity reducing means, so that a luminance signal sensed by eachpixel can be used to identify the boundary as mentioned above.

FIG. 32 is a flowchart illustrative of signal processing in a controller7 built in this electronic image pickup system.

FIG. 33 is a schematic representation of a primary color filter usedwith this electronic image pickup system.

FIG. 34 is a schematic representation of a complementary color filterused with this electronic image pickup system.

FIG. 35 is a wavelength characteristic diagram of the primary colorfilter of FIG. 33.

FIG. 36 is a wavelength characteristic diagram of the complementarycolor filter of FIG. 34.

FIG. 37 is a schematic representation of a modification to the imagepickup optical system of this embodiment, in which a color separationprism is used.

FIG. 38 is a lens section view of the first example (NumericalExample 1) of the image pickup optical system according to thisembodiment.

FIG. 39 is a diagram illustrative of the spherical aberration at thewide-angle end and chromatic aberration of magnification with respect tog-line of the image pickup optical system of FIG. 38 upon focused on aninfinite object point.

FIG. 40 is a lens section view of the second example (Numerical Example2) of the image pickup optical system according to this embodiment.

FIG. 41 is a diagram illustrative of the spherical aberration at thewide-angle end and chromatic aberration of magnification with respect tog-line of the image pickup optical system of FIG. 40 upon focused at aninfinite object point.

FIG. 42 is a schematic representation of a modification to the instantembodiment.

FIG. 43 is a schematic representation of the second embodiment of theelectronic image pickup system according to the second aspect of thepresent invention, wherein a wavelength correction filter for makingcorrection for wavelengths is used of the optical elimination of colorflares.

FIG. 44 is a diagram showing a spectral transmittance curve for thephototaking optical system alone in the image pickup optical systemaccording to the instant embodiment and a spectral transmittance curvefor the phototaking optical system plus wavelength correction filter 3.

FIG. 45 is a schematic representation illustrative of a modification tothe instant embodiment or a so-called TTL finder type observationoptical system wherein a light beam is split in front of an image pickupdevice to guide one optical path to the eyeball of an observer andanother to a finder optical system 26.

FIG. 46 is a schematic of part of another embodiment of the electronicimage pickup system according to the second aspect of the presentinvention.

FIG. 47 is a schematic representation of an image pickup optical systemthat shows one embodiment of the electronic image pickup systemaccording to the third aspect of the present invention.

FIG. 48 is a spherical aberration diagram for the image pickup opticalsystem of FIG. 47.

FIG. 49 is a schematic illustrative of the amount of displacements ofthe focal position of the image pickup optical system of FIG. 47 at themaximum height of incident ray, as viewed in a sectional view of theoptical system with the image plane at the center.

FIG. 50 is an aberration diagram for h-line chromatic aberration ofmagnification of the image pickup optical system of FIG. 47 with respectto d-line.

FIG. 51 is a schematic illustrative of the state of chromaticaberrations of the image pickup optical system of FIG. 47 at the imageheight ratios of 0.9, 0.7 and 0.5, as viewed on a paraxial image plane.

FIG. 52 is a schematic representation of the primary color filter usedwith the electronic image pickup system according to the third aspect ofthe invention.

FIG. 53 is a schematic representation of the complementary color filterused with the electronic image pickup system according to the thirdaspect of the invention.

FIG. 54 is illustrative of the wavelength characteristics of the primarycolor filter of FIG. 52.

FIG. 55 is illustrative of the spectral characteristics of thecomplementary color filter of FIG. 53.

FIGS. 56(a), 56(b) and 56(c) are sectional views illustrative of thelens arrangement of the first example of the electronic image pickupsystem according to the third aspect of the invention, each includingits optical axis, with (a), (b) and (c) illustrating the states oflenses at its wide-angle end, intermediate settings and telephoto end,respectively.

FIGS. 57(a), 57(b) and 57(c) are aberration diagrams for sphericalaberrations, astigmatism, distortion and chromatic aberrations at thewide-angle end, intermediate settings and telephoto end of the firstexample, respectively.

FIG. 58 is a sectional view of the lens arrangement of the secondexample of the electronic image pickup system according to the thirdaspect of the invention, as taken along its optical axis.

FIG. 59 is an aberration diagram for spherical aberrations, astigmatism,distortion and chromatic aberrations in the second example.

FIG. 60 is a schematic illustrative of one embodiment of the digitalcamera according to the fourth aspect of the invention.

FIG. 61 is a schematic illustrative of an example of the primary filterarrangement of the primary color filter.

FIG. 62 is a schematic illustrative of an example of the complementarycolor filter used in accordance with the fourth aspect of the invention.

FIG. 63 is a diagram illustrative of the wavelength characteristics ofFIG. 61.

FIG. 64 is a diagram illustrative of the wavelength characteristics ofFIG. 62.

FIG. 65 is a diagram illustrative of the spectral characteristics of aninfrared cutoff filter used with the first embodiment of the fourthaspect of the invention.

FIG. 66 is a diagram illustrative of the whole spectral characteristicsof the phototaking optical system comprising a complementary colorfilter according to one embodiment of the fourth aspect of theinvention.

FIG. 67 is illustrative of the R, G and B signal strength profilecalculated from the spectral characteristics of FIG. 66.

FIG. 68 is illustrative of the spectral characteristics of a generalinfrared cutoff filter.

FIG. 69 is illustrative of the whole spectral characteristics of aphototaking optical system set up with the use of the infrared cutofffilter of FIG. 68.

FIG. 70 is illustrative of the R, G and B signal strength profilecalculated from the spectral characteristics of FIG. 69.

FIG. 71 is illustrative of the spectral characteristics of a standardlight source D₆₅.

FIG. 72 is illustrative of the spectral transmittance of a phototakinglens system in one embodiment of the fourth aspect of the invention.

FIG. 73 is a schematic illustrative of the digital camera according toanother embodiment of the fourth aspect of the invention.

FIG. 74 is a schematic illustrative of the digital camera according toyet another embodiment of the fourth aspect of the invention.

FIG. 75 is a sectional view of Example A′ including its optical axis.

FIG. 76 is a sectional view of Example B′ including its optical axis.

FIG. 77 is a sectional view of Example C′ including its optical axis.

FIG. 78 is a sectional view of Example D′ including its optical axis.

FIG. 79 is a sectional view of Example E′ including its optical axis.

FIG. 80 is a sectional view of Example F′ including its optical axis.

FIG. 81 is a sectional view of Example G′ including its optical axis.

FIG. 82 is a diagram illustrative of the spectral transmittance of oneembodiment of an IR cutoff filter usable in the fourth aspect of theinvention.

FIG. 83 is an x-y chromaticity diagram illustrative of a color rangewherein color running occurs in each of the embodiments of theinvention.

FIG. 84 is a diagram illustrative of changes in the index of refractionof a single lens due to wavelengths provided that the index ofrefraction of the single lens becomes 1 at 550-nm wavelength.

FIG. 85 is a diagram illustrative of the amount of a back focal positiondisplacement with respect to wavelengths of an optical system comprisingonly a general refracting type optical elements, said amount being onthe basis of 500 nm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments and examples of the image pickup system according to thefirst aspect of the present invention are now explained with referenceto the accompanying drawings.

FIG. 1 is a schematic illustrative of a so-called digital camera 10. Alight beam emanating from an object point is subjected to imageformation by a phototaking lens system 1 made up of optical elementsmaking use of a refraction phenomenon alone to form an image on an imagepickup device 3 such as a CCD. To prevent a so-called moire phenomenonresulting from the fact that the image pickup device 3 is an array ofregularly located photoelectric converters, a filter 2 having a low-passeffect is located in front of the image pickup surface 3. In addition, afilter having an IR cutoff effect for cutting off infrared light may belocated. The light beam incident on the image pickup device 3 isconverted by the photoelectric converters to electric signals, which arethen entered into a controller 4. The electric signals are subjected atthe controller 4 to signal processing such as gamma correction or imagecompression processing, and sent via a built-in memory 5 and aninterface 7 to a personal computer 8 or the like. The resulting signalsmay be transmitted from the controller 4 to a liquid crystal monitor 6which makes it possible for the operator to check up the image to bephototaken or the phototaken image. Alternatively, image data may betransmitted from the built-in memory 5 to an auxiliary memory 9 such asa so-called smart medium (trade mark). In this embodiment, the imagepickup system is constructed such that the 400-nm wavelengthinput/output ratio is preferably 5% or less, and more preferably 2% orless, with respect to the input/output ratio for a wavelength of 400 nmto 700 nm incident on the phototaking optical system 1 at which theratio of the output signal strength with respect to the input quantityof light is high (the ratio of the output signal strength with respectto the input quantity of light).

Alternatively, the image pickup system may be constructed such that the420-nm wavelength input/output ratio is preferably 10% or greater, morepreferably 15% or greater and more preferably 20% or greater withrespect to the input/output ratio for the wavelength of 400 nm to 700 nmat which the ratio of the output signal strength with respect to theinput quantity of light is high (the ratio of the output signal strengthwith respect to the input quantity of light).

To obtain a color image, a color filter having such a filter arrangementas shown in FIG. 2 or 3 is located in front of the image pickup deviceso as to achieve a photoelectric conversion device having at least threedifferent wavelength characteristics. The filter shown in FIG. 2 is ofthe type called a primary color filter comprising red (R), green (G) andblue (B) filter elements. The respective wavelength characteristics ofthese filter elements are shown in FIG. 4. The filter shown in FIG. 3 isof the type called a complementary color filter comprising cyan (C),magenta (M) and yellow (Ye) filter elements. The respective wavelengthcharacteristics of these filter elements are shown in FIG. 5. When thecomplementary color filter is used as the filter, the filtered light isconverted by the controller 4 to R, G and B according to the followingprocessing:

for luminance signalsY=|G+M+Ye+C|*¼for color signalsR−Y=|(M+Ye)−(G+C)|B−Y=|(M+C)−(G+Ye)|With the primary color filter, it is easy to carry out processing forcolor reproduction, and with the complementary color filter, it ispossible to increase the quantity of light with respect to thephotoelectric conversion surface.

The color image may also be obtained by locating a color separationfilter on the image side of the phototaking lens system 1 to form imageson three or more image pickup elements. In FIG. 6, light is separatedinto R, G and B. More specifically, a light beam emanating from anobject point is subjected to image formation by the phototaking lenssystem 1 made up of optical elements making use of a refractionphenomenon alone, and then separated by a color separation prism 11 intoR, G and B, said prism 11 comprising a first prism element 11 ₁, asecond prism element 11 ₂ and a third prism element 11 ₃ with a dichroicmirror applied on the interface between adjacent prism elements. Thethus color-separated R, G and B image-formation light beams form imageson R, G and B phototaking image pickup elements 3 R, 3 G and 3 B,respectively.

FIG. 7 shows a modification to the FIG. 1 embodiment, using a so-calledTTL finder type wherein a light beam is split by a half-silvered mirrorprism 12 located on the object side of an image pickup element 3 forguidance to a finder optical system 13. This type is characterized inthat a subject can be observed with reduced power consumption. Betweenthe finder optical system and a phototaking system, the ratio of a lightbeam emerging from the optical path splitter means 12 toward the imagepickup element 3 with respect to a light beam incident on the opticalpath splitter means 12 may be set at less than 1 at 400-nm wavelength.In the FIG. 7 embodiment, the image pickup device 3 is located on thetransmission side and the finder optical system 13 is positioned on theopposite side. However, it is noted that it is acceptable to locate theimage pickup device on the opposite side and dispose the finder opticalsystem on the transmission side.

Here the strength of the signal produced from the image pickup device inresponse to the incident light beam is defined as the output signalstrength ratio. In an image pickup device having spectral sensitivitycharacteristics with respect to every image formation, too, it isdesired that the 400-nm wavelength input/output ratio be preferably 10%or less, more preferably 5% or less and even more preferably 2% or lesswith respect to the input/output ratio for a 400-nm to 700-nm wavelengthat which the ratio of the output signal strength with respect to theinput quantity of light (the output signal strength ratio with respectto the input quantity of light) is high.

For these embodiments, a color filter having such characteristics asshown in FIG. 8 or FIG. 9 may be used. Referring to FIG. 9, the filterhaving such characteristics shown in FIG. 5 is superposed on the filterhaving such characteristics as shown in FIG. 10, so that thecharacteristics of magenta can be easily achieved.

As shown in FIG. 11, the transmittance of the image pickup lens may bedesigned such that the sensitivity of the lens to 400-nm wavelength iskept low while the sensitivity of the lens to 420-nm wavelength ismaintained intact. Then, a transmittance control filter 14 may be spacedaway from the object side of the image pickup device 3 as shown in FIG.12. Alternatively, this control function may be offloaded from thefilter 14 and placed on other filter. It is also acceptable to apply anantireflection coating having such characteristics as shown in FIG. 13on a lens element that forms a phototaking lens system. This coating maybe applied on the lens element by the evaporation of materials such asMgF₂ and SiO₂ in an appropriately multilayered form.

In another embodiment, a phototaking lens system 1 may be detachablefrom a body including an image pickup device 3 as shown in FIG. 14. Amount 15 used to this end, for instance, may be of either the screwcoupling type or the bayonet coupling type. Then, control oftransmittance with respect to 400-nm and 420-nm wavelengths may becarried out by the phototaking lens system 1. Alternatively, control ofoutput signals with respect to incident light of 400-nm and 420-nmwavelengths may be carried out with the body including image pickupdevice 3. By controlling the 400-nm and 420-nm wavelength transmittancewith the phototaking lens system 1, for instance, it is possible toachieve the economies of mass production of image pickup devices 3. Forapplications where the quantity of light on the short wavelength side inparticular must be ensured depending on color reproducibility, anotherphototaking lens system may be provided. By controlling the outputsignals with respect to incident light of 400-nm and 420-nm wavelengthswith the body including image pickup device 3, it is possible to achievesatisfactory color reproduction with high image-formation capability,even when a conventional phototaking lens system is used.

Set out below are Examples A through F of the optical system suitablefor use with the aforesaid embodiments of the present invention. Someexamples use filters and some do not; the filters may be optionallyused.

FIGS. 15 to 17 are sectional views of Examples A to C, each including anoptical axis. Likewise, FIGS. 18 to 20 are sectional views of Examples Dto F, each including an optical axis at a wide-angle end. Examples A toC are each directed to a lens system having a fixed focal length whileExamples D to F are each directed to a zoom lens system having avariable focal length. In each figure, F denotes filters and prisms, andI stands for an image plane. Example B is suitable for slimming down acamera because a reflecting member R is located within an image pickupoptical system. Alternatively, the reflectivity of this reflectingmember R may be designed such that the reflectance of member R at a420-nm wavelength is kept intact while the reflectance of member 4 at a400-nm wavelength is reduced. Example D is suitable for use with theso-called TTL finder type or the triple type using a color separationprism.

The lens arrangement of each example is now explained.

The lens system of Example A consists of four groups or five lenses,i.e., a positive meniscus lens convex on its object side, a negativemeniscus lens convex on its object side, a stop, a doublet composed of adouble-concave lens and a double-convex lens and a double convex lens,as shown in FIG. 15. One aspherical surface is used at the object-sidesurface of the double-convex lens located nearest to the image planeside of the system.

The lens system of Example B consists of four groups or five lenses,i.e., a negative meniscus lens convex on its object side, a reflectingsurface R for turning back an optical path, a stop, a double-convexlens, a doublet composed of a double-convex lens and a double-concavelens and a positive lens having a strong convex surface on its imageside, as shown in FIG. 16. Two aspherical surfaces are used, one at thesurface of the double-convex lens located in the rear of the stop andanother at the surface of the positive lens located nearest to the imageplane side of the system.

The system of Example C consists of five groups or six lenses, i.e., twonegative meniscus lenses, each convex on its object side, a convex lens,a stop, a doublet composed of a double-concave lens and a double-convexlens, and a double-convex lens, as shown in FIG. 17. Two asphericalsurfaces are used, one at the surface of the second negative meniscuslens and another at the surface of the double-convex lens locatednearest to the image plane side of the system.

The system of Example D consists of four groups G1 to G4. As shown inFIG. 18, the first group G1 consists of three lenses or a doubletcomposed of a negative meniscus lens convex on its object side and apositive meniscus lens convex on its object side and a positive meniscuslens convex on its object side, the second group G2 consists of fourlenses or a negative meniscus lens convex on its object side, adouble-concave lens and a doublet composed of a double-concave lens anda positive meniscus lens convex on its object side, in the rear of whicha stop S is located, the third group G3 consists of three lenses or apositive meniscus lens convex on its object side, a double-convex lensand a negative meniscus lens convex on its object side, and the fourthgroup G4 consists of four lenses or a doublet composed of a negativemeniscus lens convex on its image plane side and a positive meniscuslens convex on its image plane side and two double-convex lenses. Twoaspherical surfaces are used, one at the object-side surface of thedouble-convex lens in the third group G3 and another at the surface ofthe lens in the fourth group G4, which is located nearest to the imageplane side of the system. For zooming from the wide-angle end to thetelephoto end of the system, the second group G2 moves from the objectside to the image plane side and the third and fourth groups G3 and G4move from the image plane side to the object side, as indicated byarrows, while the first group G1 and stop S remain fixed.

The system of Example E consists of four lens groups G1 to G4. As shownin FIG. 19, the first group G1 consists of one convex lens, the secondgroup G2 consists of a negative meniscus lens convex on its object sideand a doublet composed of a double-concave lens and a positive meniscuslens convex on its object side, in the rear of which a stop S islocated, the third group G3 consists of a double-convex lens and adoublet composed of a positive meniscus lens convex on its object sideand a negative meniscus lens convex on its object side, and the fourthgroup G4 consists of one double-convex lens. Two aspherical surfaces areused, one at the surface of the lens in the third group G3, which islocated nearest to the object side of the system, and another at thesurface of the lens in the fourth group G4, which is located nearest tothe object side of the system. For zooming from the wide-angle end tothe telephoto end of the system, the second group G2 moves from theobject side to the image plane side and the third and fourth groups G3and G4 move from the image plane side to the object side with theseparation between them becoming wide, as indicated by arrows, while thefirst group G1 and stop S remain fixed.

The system of Example F consists of four groups G1 to G4. As shown inFIG. 20, the first group G1 consists of one positive lens convex on itsobject side, the second group G2 consists of a negative meniscus lensconvex on its object side, a double-concave lens and a positive lenshaving a strong convex surface on its object side, in the rear of whichthere is a stop S, the third group G3 consists of a double-convex lensand a negative meniscus lens convex on its object side, and the fourthgroup G4 consists of one positive lens having a strong convex surface onits image plane side. One aspherical surface is used at the object-sidesurface of the positive lens in the fourth group G4. For zooming fromthe wide-angle end to the telephoto end of the system, the second groupG2 moves from the object side to the image plane side and the third andfourth groups G3 and G4 move from the image plane side to the objectside, as indicated by arrows, while the first group G1 and stop S remainfixed.

Enumerated below are numerical data about each example. The symbols usedhereinafter but not referred to hereinbefore have the followingmeanings.

FNO: F-number,

2ω: field angle,

p: pixel pitch,

r₁, r₂, . . . : radius of curvature of each lens surface,

d₁, d₂, . . . : separation between adjacent lenses,

n_(d1), n_(d2), . . . : d-line refractive index of each lens,

n_(g1), n_(g2), . . . : g-line refractive index of each lens,

n_(h1), n_(h2), . . . : h-line refractive index of each lens,

ΔθRN1 , ΔθRN2 , . . . : value of ΔθRN of each lens, and

ν_(d1), ν_(d2), . . . : d-line Abbe number of each lens.

The radii of curvature and separations are given by the mm unit. Herelet x represent an optical axis provided that the direction ofpropagation of light is defined as positive and y represent thedirection perpendicular to the optical axis. Then, asphericalconfiguration is given byx=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ Y ⁶ +A ₈ Y ⁸ +A ₁₀ Y¹⁰ +A ₁₂ y ¹²where r is the paraxial radius of curvature, K is the conicalcoefficient, and A₄, A₆, A₈, A₁₀ and A₁₂ are the fourth, sixth, eighth,tenth and twelfth spherical coefficients, respectively.

EXAMPLE A

f = 5.55 F_(NO) = 2.88 2ω = 64.4° p = 4.15 μm D = 6.64 r₁ = 13.9598 d₁ =2.4200 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 56.3701 d₂ = 0.2700 r₃ =7.6185 d₃ = 0.8700 n_(d2) = 1.48749 ν_(d2) = 70.21 r₄ = 2.4917 d₄ =3.3154 r₅ = ∞ (Stop) d₅ = 1.0735 r₆ = −8.2879 d₆ = 0.8000 n_(d3) =1.84666 ν_(d3) = 23.78 r₇ = 10.5000 d₇ = 3.7900 n_(d4) = 1.72916 ν_(d4)= 54.68 r₈ = −5.2842 d₈ = 0.1500 r₉ = 9.8776 (Aspheric) d₉ = 3.3700n_(d5) = 1.56384 ν_(d5) = 60.67 r₁₀ = −13.3796 d₁₀ = 2.7100 r₁₁ = ∞ d₁₁= 2.3200 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₂ = ∞ d₁₂ = 1.6000 r₁₃ = ∞d₁₃ = 0.8000 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₄ = ∞ d₁₄ = 1.0048 r₁₅ =∞ (Image plane) n_(g1) = 1.89419 n_(h1) = 1.91428 Δθ_(RN1) = +0.0174n_(g2) = 1.49596 n_(h2) = 1.49898 Δθ_(RN2) = +0.0022 n_(g3) = 1.89419n_(h3) = 1.91428 Δθ_(RN3) = +0.0174 n_(g4) = 1.74570 n_(h4) = 1.75173Δθ_(RN4) = −0.0086 n_(g5) = 1.57532 n_(h5) = 1.57947 Δθ_(RN5) = −0.0031n_(g6) = 1.52621 n_(h6) = 1.52977 Δθ_(RN6) = −0.0024 n_(g7) = 1.52621n_(h7) = 1.52977 Δθ_(RN7) = −0.0024 Aspherical Coefficients 9th surfaceK = 0 A₄ = −3.6930 × 10⁻⁴ A₆ = 7.0898 × 10⁻⁷ (3) _(S)R_(RN)/D = 1.248177(4) n_(RN) = 1.84666 (5) ν_(RN) = 23.78 (6) Δθ_(RN) = +0.0174

EXAMPLE B

f = 9.88 F_(NO) = 2.8 2ω = 59.12° p = 3.9 μm D = 11 r₁ = 42.746 d₁ =1.80 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = 9.841 d₂ = 21.36 r₃ = ∞ (Stop)d₃ = 5.09 r₄ = 96.670 d₄ = 4.16 n_(d2) = 1.69350 ν_(d2) = 53.20 r₅ =−14.943 (Aspheric) d₅ = 0.08 r₆ = 9.051 d₆ = 6.95 n_(d3) = 1.62041ν_(d3) = 60.29 r₇ = −33.014 d₇ = 0.98 n_(d4) = 1.80518 ν_(d4) = 25.42 r₈= 5.859 d₈ = 4.21 r₉ = −51.618 d₉ = 5.06 n_(d5) = 1.58913 ν_(d5) = 61.28r₁₀ = −7.361 (Aspheric) d₁₀ = 1.50 r₁₁ = ∞ d₁₁ = 1.00 n_(d6) = 1.51633ν_(d6) = 64.14 r₁₂ = ∞ d₁₂ = 1.60 n_(d7) = 1.54771 ν_(d7) = 62.84 r₁₃ =∞ n_(g1) = 1.49596 n_(h1) = 1.49898 Δθ_(RN1) = +0.0022 n_(g2) = 1.70972n_(h2) = 1.71556 Δθ_(RN2) = −0.0081 n_(g3) = 1.63315 n_(h3) = 1.63778Δθ_(RN3) = −0.0012 n_(g4) = 1.84729 n_(h4) = 1.86494 Δθ_(RN4) = +0.0158n_(g5) = 1.60103 n_(h5) = 1.60535 Δθ_(RN5) = −0.0018 n_(g6) = 1.52621n_(h6) = 1.52977 Δθ_(RN6) = −0.0024 n_(g7) = 1.55843 n_(h7) = 1.56226Δθ_(RN7) = −0.0045 Aspherical Coefficients 5th surface K = 0 A₄ =6.18542 × 10⁻⁵ A₆ = 3.07784 × 10⁻⁷ 10th surface K = 0 A₄ = 4.92151 ×10⁻⁴ A₆ = −3.57904 × 10⁻⁶ A₈ = 4.22919 × 10⁻⁸ (3) _(S)R_(RN)/D =0.532636 (4) n_(RN) = 1.80518 (5) ν_(RN) = 25.42 (6) Δθ_(RN) = +0.0158

EXAMPLE C

f = 4.4182 F_(NO) = 2.4 2ω = 80.9° p = 4.15 μm or 3 μm D = 6.64 r₁ =13.2550 d₁ = 0.9000 n_(d1) = 1.60311 ν_(d1) = 60.64 r₂ = 7.0317 d₂ =1.0000 r₃ = 12.0000 (Aspheric) d₃ = 0.8000 n_(d2) = 1.56384 ν_(d2) =60.67 r₄ = 4.9103 d₄ = 4.6372 r₅ = 7.9159 d₅ = 1.1424 n_(d3) = 1.84666ν_(d3) = 23.78 r₆ = ∞ d₆ = 0.5000 r₇ = ∞ (Stop) d₇ = 1.8751 r₈ = −3.7652d₈ = 1.0000 n_(d4) = 1.80518 ν_(d4) = 25.42 r₉ = 8.7546 d₉ = 2.1667n_(d5) = 1.72916 ν_(d5) = 54.68 r₁₀ = −4.8805 d₁₀ = 0.1500 r₁₁ = 10.0186(Aspheric) d₁₁ = 2.2298 n_(d6) = 1.56384 ν_(d6) = 60.67 r₁₂ = −8.4667d₁₂ = 2.3588 r₁₃ = ∞ d₁₃ = 1.9000 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₄ =∞ d₁₄ = 0.8000 n_(d8) = 1.51633 ν_(d8) = 64.14 r₁₅ = ∞ d₁₅ = 1.2000 r₁₆= ∞ d₁₆ = 0.7500 n_(d9) = 1.48749 ν_(d9) = 70.23 r₁₇ = ∞ d₁₇ = 1.2200r₁₈ = ∞ (Image plane) n_(g1) = 1.61541 n_(h1) = 1.61987 Δθ_(RN1) =−0.0019 n_(g2) = 1.57532 n_(h2) = 1.57947 Δθ_(RN2) = −0.0031 n_(g3) =1.89419 n_(h3) = 1.91428 Δθ_(RN3) = +0.0174 n_(g4) = 1.84729 n_(h4) =1.86494 Δθ_(RN4) = +0.0158 n_(g5) = 1.74570 n_(h5) = 1.75173 Δθ_(RN5) =−0.0086 n_(g6) = 1.57532 n_(h6) = 1.57947 Δθ_(RN6) = −0.0031 n_(g7) =1.52621 n_(h7) = 1.52977 Δθ_(RN7) = −0.0024 n_(g8) = 1.52621 n_(h8) =1.52977 Δθ_(RN8) = −0.0024 n_(g9) = 1.49596 n_(h9) = 1.49898 Δθ_(RN9) =+0.0022 Aspherical Coefficients 3rd surface K = 0 A₄ = 3.1698 × 10⁻⁴ A₆= 6.1083 × 10⁻⁵ A₈ = −4.6332 × 10⁻⁶ A₁₀ = −1.4286 × 10⁻⁷ 11th surface K= 0 A₄ = −1.0432 × 10⁻³ A₆ = −2.9351 × 10⁻⁵ A₈ = 4.2352 × 10⁻⁶ A₁₀ =−1.8071 × 10⁻⁷ (3) _(S)R_(RN)/D = 0.567048 (4) n_(RN) = 1.80518 (5)ν_(RN) = 25.42 (6) Δθ_(RN) = +0.0158

EXAMPLE D

f = 9.099˜18.100˜35.998 F_(NO) = 2.008˜2.065˜2.481 2ω =68.4°˜35.8°˜18.6° p = 3.9 μm D = 11 r₁ = 74.1213 d₁ = 2.5000 n_(d1) =1.84666 ν_(d1) = 23.78 r₂ = 45.2920 d₂ = 7.6976 n_(d2) = 1.61800 ν_(d2)= 63.33 r₃ = 200.0000 d₃ = 0.1500 r₄ = 53.6322 d₄ = 5.1636 n_(d3) =1.77250 ν_(d3) = 49.60 r₅ = 160.3763 d₅ = (Variable) r₆ = 86.4469 d₆ =1.8938 n_(d4) = 1.77250 ν_(d4) = 49.60 r₇ = 12.9947 d₇ = 6.5582 r₈ =−633.9388 d₈ = 1.3849 n_(d5) = 1.84666 ν_(d5) = 23.78 r₉ = 53.5036 d₉ =3.0086 r₁₀ = −70.1852 d₁₀ = 1.3000 n_(d6) = 1.48749 ν_(d6) = 70.21 r₁₁ =19.4251 d₁₁ = 4.0971 n_(d7) = 1.80518 ν_(d7) = 25.42 r₁₂ = 567.6091 d₁₂= (Variable) r₁₃ = ∞ (Stop) d₁₃ = (Variable) r₁₄ = 35.5332 d₁₄ = 2.9155n_(d8) = 1.84666 ν_(d8) = 23.78 r₁₅ = 149.5334 d₁₅ = 1.9951 r₁₆ =23.1874 d₁₆ = 3.2540 n_(d9) = 1.69350 ν_(d9) = 53.20 (Aspheric) r₁₇ =−136.5790 d₁₇ = 0.1500 r₁₈ = 54.2006 d₁₈ = 1.1258 n_(d10) = 1.80518ν_(d10) = 25.42 r₁₉ = 17.2110 d₁₉ = (Variable) r₂₀ = −12.6096 d₂₀ =1.1000 n_(d11) = 1.80518 ν_(d11) = 25.42 r₂₁ = −55.3792 d₂₁ = 3.1600n_(d12) = 1.61800 ν_(d12) = 63.33 r₂₂ = −15.6001 d₂₂ = 0.1500 r₂₃ =74.9447 d₂₃ = 3.2661 n_(d13) = 1.61800 ν_(d13) = 63.33 r₂₄ = −30.4739d₂₄ = 0.1500 r₂₅ = 124.0475 d₂₅ = 2.5117 n_(d14) = 1.69350 ν_(d14) =53.20 r₂₆ = −68.0400 d₂₆ = (Aspheric) (Variable) r₂₇ = ∞ d₂₇ = 24.0000n_(d15) = 1.51633 ν_(d15) = 64.14 r₂₈ = ∞ d₂₈ = 1.0000 r₂₉ = ∞ d₂₉ =1.5700 n_(d16) = 1.54771 ν_(d16) = 62.84 r₃₀ = ∞ d₃₀ = 1.0000 r₃₁ = ∞d₃₁ = 0.8000 n_(d17) = 1.51823 ν_(d17) = 58.96 r₃₂ = ∞ n_(g1) = 1.89419n_(h1) = 1.91428 Δθ_(RN1) = +0.0174 n_(g2) = 1.63010 n_(h2) = 1.63451Δθ_(RN2) = +0.0051 n_(g3) = 1.79197 n_(h3) = 1.79917 Δθ_(RN3) = −0.0092n_(g4) = 1.79197 n_(h4) = 1.79917 Δθ_(RN4) = −0.0092 n_(g5) = 1.89419n_(h5) = 1.91428 Δθ_(RN5) = +0.0174 n_(g6) = 1.49596 n_(h6) = 1.49898Δθ_(RN6) = +0.0022 n_(g7) = 1.84729 n_(h7) = 1.86494 Δθ_(RN7) = +0.0158n_(g8) = 1.89419 n_(h8) = 1.91428 Δθ_(RN8) = +0.0174 n_(g9) = 1.70972n_(h9) = 1.71566 Δθ_(RN9) = −0.0081 n_(g10) = 1.84729 n_(h10) = 1.86494Δθ_(RN10) = +0.0158 n_(g11) = 1.84729 n_(h11) = 1.86494 Δθ_(RN11) =+0.0158 n_(g12) = 1.63010 n_(h12) = 1.63451 Δθ_(RN12) = +0.0051 n_(g13)= 1.63010 n_(h13) = 1.63451 Δθ_(RN13) = +0.0051 n_(g14) = 1.70972n_(h14) = 1.71566 Δθ_(RN14) = −0.0081 n_(g15) = 1.52621 n_(h15) =1.52977 Δθ_(RN15) = −0.0024 n_(g16) = 1.55843 n_(h16) = 1.56226Δθ_(RN16) = −0.0045 n_(g17) = 1.52915 n_(h17) = 1.53314 Δθ_(RN17) =+0.0035 Zooming Spaces f 9.099 18.100 35.998 d₅ 1.006 18.105 28.360 d₁₂28.950 11.850 1.597 d₁₃ 12.005 9.317 1.499 d₁₉ 7.213 7.088 10.629 d₂₆1.500 4.313 8.589 Aspherical Coefficients 16th surface K = 0 A₄ =−1.3659 × 10⁻⁵ A₆ = −5.3156 × 10⁻⁹ A₈ = −2.4548 × 10⁻¹¹ A₁₀ = 2.2544 ×10⁻¹² 26th surface K = 0 A₄ = 6.6763 × 10⁻⁶ A₆ = 3.7977 × 10⁻⁸ A₈ =−4.9995 × 10⁻¹⁰ A₁₀ = 2.3437 × 10⁻¹² (3) _(S)R_(RN)/D = 1.5645 1.14632(4) n_(RN) = 1.80518 1.80518 (5) ν_(RN) = 25.42 25.42 (6) Δθ_(RN) =+0.0158 +0.0158

EXAMPLE E

f = 6.608˜11.270˜19.098 F_(NO) = 2.03˜2.36˜2.91 p = 3.9 μm D = 8 r₁ =36.688 d₁ = 4.14 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = ∞ d₂ = (Variable)r₃ = 21.750 d₃ = 1.25 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ = 8.054 d₄ =5.45 r₅ = −27.511 d₅ = 1.00 n_(d3) = 1.48749 ν_(d3) = 70.23 r₆ = 10.412d₆ = 4.50 n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 40.550 d₇ = (Variable) r₈= ∞ (Stop) d₈ = (Variable) r₉ = 17.583 (Aspheric) d₉ = 3.42 n_(d5) =1.58913 ν_(d5) = 61.30 r₁₀ = −35.670 d₁₀ = 0.20 r₁₁ = 9.390 d₁₁ = 4.35n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ = 87.943 d₁₂ = 0.90 n_(d7) = 1.84666ν_(d7) = 23.78 r₁₃ = 6.609 d₁₃ = (Variable) r₁₄ = 13.553 d₁₄ = 3.28n_(d8) = 1.58913 ν_(d8) = 61.30 (Aspheric) r₁₅ = −30.808 n_(g1) =1.49596 n_(h1) = 1.49898 Δθ_(RN1) = +0.0022 n_(g2) = 1.89419 n_(h2) =1.91428 Δθ_(RN2) = +0.0174 n_(g3) = 1.49596 n_(h3) = 1.49898 Δθ_(RN3) =+0.0022 n_(g4) = 1.89419 n_(h4) = 1.91428 Δθ_(RN4) = +0.0174 n_(g5) =1.60103 n_(h5) = 1.60535 Δθ_(RN5) = −0.0018 n_(g6) = 1.79197 n_(h6) =1.79917 Δθ_(RN6) = −0.0092 n_(g7) = 1.89419 n_(h7) = 1.91428 Δθ_(RN7) =+0.0174 n_(g8) = 1.60103 n_(h8) = 1.60535 Δθ_(RN8) = −0.0018 ZoomingSpaces f 6.608 11.270 19.098 d₂ 1.00 9.66 15.80 d₇ 16.20 7.55 1.50 d₈8.66 5.46 1.50 d₁₃ 3.46 5.00 5.71 Aspherical Coefficients 9th surface K= 0.000 A₄ = −4.66054 × 10⁻⁵ A₆ = −1.33346 × 10⁻⁶ A₈ = 6.88261 × 10⁻⁸A₁₀ = −1.18171 × 10⁻⁹ A₁₂ = 1.21868 × 10⁻¹² 14th surface K = 0.000 A₄ =−9.93375 × 10⁻⁵ A₆ = −9.76311 × 10⁻⁷ A₈ = 3.21037 × 10⁻⁷ A₁₀ = −1.95172× 10⁻⁸ A₁₂ = 3.74139 × 10⁻¹⁰ (3) _(S)R_(RN)/D = 0.826125 (4) n_(RN) =1.84666 (5) ν_(RN) = 23.78 (6) Δθ_(RN) = +0.0174

EXAMPLE F

f = 9.000˜15.590˜27.000 F_(NO) = 2.800˜3.030˜4.069 2ω =67.094°˜39.462°˜23.030° p = 6.7 μm D = 11 r₁ = 44.5137 d₁ = 4.4000n_(d1) = 1.69680 ν_(d1) = 55.53 r₂ = 137.7320 d₂ = (Variable) r₃ =23.5602 d₃ = 1.6000 n_(d2) = 1.69680 ν_(d2) = 55.53 r₄ = 12.0406 d₄ =5.7412 r₅ = −54.8255 d₅ = 1.5000 n_(d3) = 1.56384 ν_(d3) = 60.70 r₆ =13.6238 d₆ = 3.8135 r₇ = 16.0196 d₇ = 2.2000 n_(d4) = 1.84666 ν_(d4) =23.78 r₈ = 23.3091 d₈ = (Variable) r₉ = ∞ (Stop) d₉ = (Variable) r₁₀ =31.1300 d₁₀ = 6.5179 n_(d5) = 1.77250 ν_(d5) = 49.60 r₁₁ = −15.0403 d₁₁= 0.1939 r₁₂ = −13.3787 d₁₂ = 0.8893 n_(d6) = 1.84666 ν_(d6) = 23.78 r₁₃= −65.0570 d₁₃ = (Variable) r₁₄ = −2370.3961 d₁₄ = 4.3000 n_(d7) =1.49241 ν_(d7) = 57.66 (Aspheric) r₁₅ = −14.2694 d₁₅ = (Variable) r₁₆ =∞ d₁₆ = 1.1400 n_(d8) = 1.54771 ν_(d8) = 62.84 r₁₇ = ∞ d₁₇ = 0.8100n_(d9) = 1.54771 ν_(d9) = 62.84 r₁₈ = ∞ d₁₈ = 1.0000 r₁₉ = ∞ d₁₉ =1.0000 n_(d10) = 1.48749 ν_(d10) = 70.23 r₂₀ = ∞ d₂₀ = 1.0000 r₂₁ = ∞d₂₁ = 0.8000 n_(d11) = 1.51823 ν_(d11) = 58.96 r₂₂ = ∞ n_(g1) = 1.71234n_(h1) = 1.71800 Δθ_(RN1) = −0.0082 n_(g2) = 1.71234 n_(h2) = 1.71800Δθ_(RN2) = −0.0082 n_(g3) = 1.57532 n_(h3) = 1.57947 Δθ_(RN3) = −0.0031n_(g4) = 1.89419 n_(h4) = 1.91428 Δθ_(RN4) = +0.0174 n_(g5) = 1.79197n_(h5) = 1.79917 Δθ_(RN5) = −0.0092 n_(g6) = 1.89419 n_(h6) = 1.91428Δθ_(RN6) = +0.0174 n_(g7) = 1.50320 n_(h7) = 1.50713 Δθ_(RN7) = +0.0104n_(g8) = 1.55843 n_(h8) = 1.56226 Δθ_(RN8) = −0.0045 n_(g9) = 1.55843n_(h9) = 1.56226 Δθ_(RN9) = −0.0045 n_(g10) = 1.49596 n_(h10) = 1.49898Δθ_(RN10) = +0.0022 n_(g11) = 1.52915 n_(h11) = 1.53314 Δθ_(RN11) =+0.0035 Zooming Spaces f 9.000 15.590 27.000 d₂ 1.000 13.349 18.974 d₈20.474 8.125 2.500 d₉ 13.221 9.796 2.000 d₁₃ 6.416 6.356 7.516 d₁₅15.209 18.694 25.330 Aspherical Coefficients 14th surface K = 0.0000 A₄= −7.8946 × 10⁻⁵ A₆ = 3.2441 × 10⁻⁸ A₈ = −1.6090 × 10⁻⁹ A₁₀ = 1.6631 ×10⁻¹¹ (3) _(s)R_(RN)/D = 1.21624 (4) n_(RN) = 1.84666 (5) ν_(RN) = 23.78(6) Δθ_(RN) = +0.0174

Next, embodiments of the second aspect of the present invention areexplained with reference to the accompanying drawings.

FIG. 26 is a schematic illustrative of a so-called digital camera 113that is the first embodiment of the electronic image pickup systemaccording to the second aspect of the present invention.

According to this embodiment, a light beam emanating from an objectpoint is subjected to image formation by a phototaking lens system 101′made up of an optical element making use of a refraction phenomenonalone and designed to produce chromatic aberrations, thereby forming animage on an electronic image pickup device 102 such as a CCD. To preventa so-called moire phenomenon resulting from the fact that the imagepickup device is an array of regularly located photoelectric converters(pixels), a low-pass filter 106 having a low-pass effect is located infront of the image pickup surface 104 of the electronic image pickupdevice 102. In addition, a filter having an IR cutoff effect for cuttingoff infrared light may be located depending of the designee needed.

The entrance surface of the electronic image pickup device 102 isprovided with a mosaic filter having at least three spectralcharacteristics for obtaining a color image, wherein each wavelengthrange of light beam is incident on each pixel.

The light beam incident on the electronic image pickup device 102 isconverted by the photoelectric converters or pixels to electric signalscontaining luminance information and color information, which are thenentered into a controller 107. The electric signals are subjected at thecontroller 107 to signal processing such as gamma correction or imagecompression processing, and sent via a built-in memory 108 and aninterface 109 to a personal computer 110 or the like. The resultingsignals may be transmitted from the controller 107 to a liquid crystalmonitor 111 which makes it possible for the operator to check the imageto be phototaken or the phototaken image. Alternatively, image data maybe transmitted from the built-in memory 105 to an auxiliary memory 112such as a so-called smart medium (trade mark).

The electronic image pickup system according to this embodiment ischaracterized in that an optical path splitter means comprising acemented prism 114 is located on an optical path passing through anphototaking optical system 101 and a two-dimensional area photometricsensor 115 is located as a high luminance difference boundary detectionmeans on one of the split optical paths. Then, the two-dimensional areasensor 115 is provided on its surface with an ND filter in such a waythat its sensitivity is reduced down to −3 level, i.e., ⅛ of that of theimage pickup device 102.

An image substantially identical with that on the image pickup surface104 is formed on the two-dimensional area photometric sensor 115. Thetwo-dimensional area photometric sensor 115 has a light-sensing surfacewith a plurality of photometric areas 116 regularly located thereon, asshown in FIG. 27, so that an electric signal including information aboutthe luminance of a subject can be transmitted from each photometric area116 to the controller 107.

At the controller 107, the image reading time (corresponding to ashutter speed in the case of a silver-salt camera) and relative aperture(F-number) are determined on the basis of the luminance informationincluded in the electric signal sent out of the image pickup device 3together with luminance information and color information, therebyproviding correct exposure. Alternatively, the image reading time andrelative aperture may be controlled on the basis of electric signalsfrom the two-dimensional area photometric sensor 115 including luminanceinformation rather than the luminance information form the image pickupdevice 103, thereby providing correct exposure.

Here consider the case where a high-contrast subject is phototaken in aback-light room with a clear sky in the background, using the electronicimage pickup system constructed according to the instant embodiment, asshown in FIG. 28. The condition where pixels with a luminance differenceequal to or greater than a certain level (for instance, a pixel having alight-sensing level of +2 EV or greater and a pixel having alight-sensing level of −1 EV or less) are found among a certain numberof juxtaposed pixels (for instance, 6 pixels) on the electronic imagepickup device 102 is calculated from luminance information bearingelectric signals from the two-dimensional area photometric sensor 115via the controller 107. In this case, color flares 119 become strikingto the eye due to chromatic aberrations produced by the phototakingoptical system 101.

Then, the liquid crystal monitor 111 indicates that an area having alarge luminance difference is found on the screen, thereby urging theobserver to change the camera angle and automatically popping up anelectronic flash mechanism for preparation for auxiliary illumination,so that high contrasts can be reduced for color flare reductions.Alternatively, the system may be designed to actuate a buzzer 118 tosound a beep as a warning.

When the subject is phototaken with a high-contrast area, an imagehaving large chromatic aberrations is formed on the image pickup surface104. The system is thus designed such that a boundary where theluminance difference found among a certain number of pixels reaches orexceeds a certain level is detected through the controller 107 and colorflares in the vicinity of the detected boundary (those found at theboundary and one pixel adjacent thereto) are reduced. To this end, theluminance- and color-information bearing electric signals from the imagepickup device 103 are electrically controlled.

FIG. 29 is an enlarged view of a part of the image pickup surface 104,which is illustrative of one exemplary luminance difference with respectto correct exposure for each pixel. In FIG. 29, each measure representsa pixel 120. Luminance signals from pixels 120 are analyzed to calculatean area of +2 EV or greater and an area of −1 EV or less, each withrespect to correct exposure, thereby identifying a boundary across which6 or less pixels exist. In FIG. 29, pixels corresponding to the boundaryare marked with X. Then, signal processing is carried out via thecontroller 107 in such a way as to eliminate color flares in theboundary range including pixels adjacent to the boundary (those markedwith slashes). This signal processing may be carried out in any desiredmode provided that the vicinity of the boundary can be corrected. Forinstance, it is acceptable to make correction for the boundary alone orexclude the pixels nearest to the boundary from correction.

It is here noted that, instead of using the signals from the imagepickup device, the signals from the two-dimensional area photometricsensor 115 may be used with each photometric area 116 on the photometricsensor 115 corresponding to each pixel 120, thereby identifying theboundary.

How the signal processing is carried out is now explained.

According to one exemplary signal processing method, the saturation ofan image in the vicinity of the boundary may be decreased to reduce“color running”. The “color running” makes the colors of the imageunnaturally bright, because color flares of long and short wavelengthseasily occurring from the light to dark portion make blue and redbrighter as compared with those of an actual image. This “color running”may be reduced by bringing the reproducibility of one colorcorresponding to a pixel of strong luminance down to the luminance levelof other color, thereby achieving saturation and luminance reductions.

Alternatively, the “color running” may be reduced by using thecontroller 107 as the signal processing means to control thechromaticity of the boundary and the vicinity of a portion of the darkside located adjacent to the boundary and having low luminance in such away as to bring that chromaticity close to the chromaticity of a portionof the dark side spaced away from the boundary by a certain number ofpixels (for instance, 2 pixels).

The boundary having a large luminance difference may also be detected byproducing correct exposure via the controller 107 and using atwo-dimensional area photometric sensor 115 shown in FIG. 30simultaneously with or before or after phototaking to detect pixelscorresponding to an area (hatched) where the exposure level is saturatedupon 3 EV-underexposure with respect to correct exposure and unsaturatedpixels adjacent to the saturated pixels, so that pixels between thesearea can be identified as the boundary having a large luminancedifference.

Instead of the two-dimensional area photometric sensor 115 shown in FIG.26, it is acceptable to use an electronic image pickup device 102 which,as shown in FIG. 31, is provided on an image pickup surface 104 with aplurality of photometric areas 116 acting as pixels, each provided withan ND filter as a sensitivity reducing means. Then, the boundary may bedetected as mentioned above, using luminance information included in anelectric signal containing information about the luminance of lightsensed by each pixel.

FIG. 32 is a schematic flowchart of the signal processing in thecontroller 107. As shown in FIG. 32, electric signals containinginformation about the luminance and color of light sensed by the pixelsof the electronic image pickup device are converted by a circuit blockto luminance signals and color signals. These luminance signals and/orcolor signals are also embraced in the concept of electric signalscontaining information about luminance and color used in the presentdisclosure.

A color filter used with the electronic image pickup device 102 is nowexplained.

To obtain a color image, a color filter having such a filter arrangementas shown in FIG. 33 or 34 is located in front of the image pickup deviceso as to achieve a photoelectric conversion device having at least threedifferent wavelength characteristics. The filter shown in FIG. 33 is ofthe type called a primary color filter comprising red (R), green (G) andblue (B) filter elements. The respective wavelength characteristics ofthese filter elements are shown in FIG. 35. The filter shown in FIG. 34is of the type called a complementary color filter comprising cyan (C),magenta (M), yellow (Ye) and green (G) filter elements. The respectivewavelength characteristics of these filter elements are shown in FIG.36.

When the complementary color filter is used as the filter, C, M, Ye andG are converted by a controller 7 to R, G and B according to thefollowing processing:

for luminance signalsY=|G+M+Ye+C|×¼for color signalsR−Y=|(M+Ye)−(G+C)|B−Y=|(M+C)−(G+Ye)|With the primary color filter, it is easy to carry out colorreproduction processing, and with the complementary color filter, it ispossible to increase the quantity of light with respect to thephotoelectric conversion surface.

The color image may also be obtained by locating a color separationprism 124—which comprises a first prism 120, a second prism 121 and athird prism 123 as an example—on the image side of a phototaking lenssystem 101, by which light from the phototaking optical system isseparated into R, G and B to form images on three or more image pickupelements 102R, 102G and 102G.

Examples of the chromatic aberration-producing image pickup opticalsystem used with the aforesaid construction are now given in the form ofnumerical data.

EXAMPLE 1

FIG. 38 is a lens section view of the first example (NumericalExample 1) of the image pickup optical system according to thisembodiment, and FIG. 39 is a diagram illustrative of the sphericalaberration at the wide-angle end and chromatic aberration ofmagnification with respect to g-line of the image pickup optical systemof FIG. 38 upon focused at infinity.

In the following numerical data, r₁, r₂, r₃, . . . are the radii ofcurvature of lens surfaces, d1, d2, d₃, . . . are the thicknesses or airseparations of lenses, n₁, n₂, n₃, . . . are the d-line (587.56 nm)refractive indices of lenses, and ν₂, ν₂, ν₃, . . . are the Abbe'snumbers of lenses.

Here let z represent an optical axis direction and y represent thedirection perpendicular to the optical axis. Then, asphericalconfiguration is given byz=(y ² /r)/[1+√{1−(1+k)·(y/r)² }]+AC ₂ y ² AC ₄ y ⁴ +AC ₆ Y ⁶ +AC ₈ y ⁸+AC ₁₀ y ¹⁰ +AC ₁₂ y ¹²where r is the paraxial radius of curvature, K is the conicalcoefficient, and AC₂, AC₄, AC₆, AC₈, AC₁₀ and AC₁₂ are the sphericalcoefficients, respectively.

In the following numerical data, the minimum pixel pitch of theelectronic image pickup device is P=0.003 mm.

The numerical data about this example are given in the form of NumericalExample 1.

NUMERICAL EXAMPLE 1

Fmin = 2.039 Focal length 6.5 mm-19.5 mm F-number 2.039-2 Upon focusedon an infinite object point r₁ = 36.6880 d₁ = 4.1400 n₁ = 1.48749 ν₁ =70.23 r₂ = ∞ d₂ = variable r₃ = 21.7500 d₃ = 1.2500 n₃ = 1.84666 ν₃ =23.78 r₄ = 8.0540 d₄ = 5.4500 r₅ = −27.5110 d₅ = 1.0000 n₅ = 1.48749 ν₅= 70.23 r₆ = 10.4120 d₆ = 4.5000 n₆ = 1.84666 ν₆ = 23.78 r₇ = 40.5500 d₇= variable r₈ = ∞ (stop) d₈ = variable r₉ = 17.5830 (aspheric) d₉ =3.4200 n₉ = 1.58913 ν₉ = 61.30 r₁₀ = −35.6700 d₁₀ = 0.2000 r₁₁ = 9.3900d₁₁ = 4.3500 n₁₁ = 1.77250 ν₁₁ = 49.60 r₁₂ = 87.9430 d₁₂ = 0.9000 n₁₂ =1.84666 ν₁₂ = 23.78 r₁₃ = 6.6090 d₁₃ = variable r₁₄ = 13.5530 (aspheric)d₁₄ = 3.2800 n₁₄ = 1.58913 ν₁₄ = 61.30 r₁₅ = −30.8080 d₁₅ = variable r₁₆= ∞ d₁₆ = 0.8000 n₁₆ = 1.51633 ν₁₆ = 64.14 r₁₇ = ∞ d₁₇ = 1.8000 n₁₇ =1.54771 ν₁₇ = 62.84 r₁₈ = ∞ d₁₈ = 0.8000 r₁₉ = ∞ d₁₉ = 0.7500 n₁₉ =1.51633 ν₁₉ = 64.14 r₂₀ = ∞ d₂₀ = variable Electronic image pickupdevice ∞ Ninth surface k = 0. AC₂ = 0.0000 AC₄ = −4.6605 × 10⁻⁵ AC₆ =−1.3335 × 10⁻⁶ AC₈ = 6.8826 × 10⁻⁸ AC₁₀ = −1.1817 × 10⁻⁹ AC₁₂ = 1.2187 ×10⁻¹² Fourteenth Surface k = 0. AC₂ = 0.0000 AC₄ = −9.9337 × 10⁻⁵ AC₆ =−9.7631 × 10⁻⁷ AC₈ = 3.2104 × 10⁻⁷ AC₁₀ = −1.9517 × 10⁻⁸ AC₁₂ = 3.7414 ×10⁻¹⁰ Surface separation Wide-Angle Intermediate Focal Telephoto SurfaceNo. End Length End  2 1.00000 9.66000 15.80000  7 16.20000 7.550001.50000  8 8.66000 5.46000 1.50000 13 3.46000 5.00000 5.71000 15 3.392005.16000 8.51000 20 1.16922 1.01169 0.91052 Vitreous Material 435.84404.656 Surface No. (OHARA trade mark) g-line RI h-line RI  1 S-FSL5-01.49596 1.49898  3 S-TIH53-0 1.89418 1.91428  5 S-FSL5-0 1.49596 1.49898 6 S-TIH53-0 1.89418 1.91428  9 BACD5-H 1.60100 1.60531 11 S-LAH66-01.79197 1.79917 12 S-TIH53-0 1.89418 1.91428 14 BACD5-H 1.60100 1.6053116 S-BSL7-0 1.52621 1.52977 17 BAL21-0 1.55843 1.56226 19 S-BSL7-01.52621 1.52977 RI: Refractive index Amounts of aberrations Lh = 0.0865mm Lg = 0.0324 mm Ld = 0.0061 mm (Lh − Ld)/Fmin = 0.0394 mm = 13.1P When(Lλ − Ld)/Fmin = 0.05 mm, Lλ = 0.0959 mm λ1 = 401 nm When (Lλ − Ld)/Fmin= 0.04 mm, Lλ = 0.0755 mm λ1 = 409 nm When (Lλ − Ld)/Fmin = 0.03 mm, Lλ= 0.0551 mm λ1 = 420 nm |Sh| = 0.0218 mm = 7.3P |Sg| = 0.0083 mm When|Sλ| = 0.025 mm, λ2 = 400 nm When |Sλ| = 0.02 mm, λ2 = 408 nm When |Sλ|= 0.015 mm, λ2 = 418 nm

EXAMPLE 2

FIG. 40 is a lens section view of the second example of the image pickupoptical system according to this embodiment, and FIG. 41 is a diagramillustrative of the spherical aberration and chromatic aberration ofmagnification with respect to d-line of the image pickup optical systemupon focused at infinity.

In the second example, axial chromatic aberrations are well corrected,but chromatic aberrations of magnification remain undercorrected.

The numerical data about this example are given in the form of NumericalExample 1.

NUMERICAL EXAMPLE 1

Fmin = 2.881 Focal length 5.56 mm F-number 2.881 Upon focused on aninfinite object point r₁ = 14.0020 d₁ = 2.4200 n₁ = 1.84666 ν₁ = 23.78r₂ = 56.9710 d₂ = 0.2500 r₃ = 8.4400 d₃ = 0.8700 n₃ = 1.48749 ν₃ = 70.21r₄ = 2.5510 d₄ = 2.4300 r₅ = ∞ d₅ = 1.0000 r₆ = ∞ d₆ = 1.2000 r₇ =−8.7540 d₇ = 0.8000 n₇ = 1.84666 ν₇ = 23.78 r₈ = 10.5000 d₈ = 3.7700 n₈= 1.72916 ν₈ = 54.68 r₉ = −5.4690 d₉ = 0.1500 r₁₀ = 10.2500 (aspheric)d₁₀ = 3.3300 n₁₀ = 1.56384 ν₁₀ = 60.67 r₁₁ = −12.6780 d₁₁ = 2.0000 r₁₂ =∞ d₁₂ = 1.9100 n₁₂ = 1.51633 ν₁₂ = 64.14 r₁₃ = ∞ d₁₃ = 0.8000 n₁₃ =1.51633 ν₁₃ = 64.14 r₁₄ = ∞ d₁₄ = 1.8700 r₁₅ = ∞ d₁₅ = 0.7500 n₁₅ =1.48749 ν₁₅ = 70.23 r₁₆ = ∞ d₁₆ = 1.4633 Electronic image pickup device∞ Tenth surface k = 0. AC₂ = 0.0000 AC₄ = −3.6137 × 10⁻⁴ AC₆ = 6.0453 ×10⁻⁷ AC₈ = 0.0000 AC₁₀ = 0.0000 AC₁₂ = 0.0000 Vitreous Material 435.84404.656 Surface No. (OHARA trade mark) g-line RI h-line RI  1 S-TIH53-01.89416 1.91428  3 S-FSL5-0 1.49597 1.49898  7 S-TIH53-0 1.89416 1.91428 8 S-LAL18-0 1.74570 1.75173 10 S-BAL41-0 1.57532 1.57947 12 S-BSL7-01.52621 1.52977 13 S-BSL7-0 1.52621 1.52977 15 S-FSL5-0 1.49596 1.49898RI: Refractive index Amounts of aberrations Lh = 0.02972 mm Lg = 0.04734mm Ld = 0.04041 mm (Lh − Ld)/Fmin = −0.003 mm = −1P When (Lλ − Ld)/Fmin= 0.05 mm, Lλ = 0.1036 mm λ1 = 344 nm When (Lλ − Ld)/Fmin = 0.04 mm, Lλ= 0.0748 mm λ1 = 351 nm When (Lλ − Ld)/Fmin = 0.03 mm, Lλ = 0.0460 mm λ1= 360 nm |Sh| = 0.0226 mm = 7.5P |Sg| = 0.0100 mm When |Sλ| = 0.025 mm,λ2 = 400 nm When |Sλ| = 0.02 mm, λ2 = 409 nm When |Sλ| = 0.015 mm, λ2 =420 nm

As shown in FIG. 42, the electronic image pickup system according to theinstant embodiment may have a mount 125 so as to detachably mount aphototaking optical system 101 on an electronic image pickup system body113 including an electronic image pickup device 102. It is thus possibleto mount a variety of phototaking optical systems 101 on the electronicimage pickup system depending on phototaking conditions, and makecorrection for color flares in various states. It is here noted that themount 125 may be of the screw coupling type or the bayonet couplingtype. Otherwise, this electronic image pickup system is fundamentallysimilar to the image pickup system shown in FIG. 26.

With the instant embodiment of the second aspect of the presentinvention, it is possible to control the luminance or color signals ofthe image to be phototaken, thereby reducing the “color running”, evenwhen chromatic aberrations are produced as a result of slimming down thephototaking optical system.

The second embodiment of the second aspect of the present invention isshown in FIG. 43. The same parts as in the first embodiment areindicated by the same references, and so their detailed explanations areomitted.

The electronic image pickup system according to this embodiment isdesigned in such a way as to optically eliminate color flares by use ofa wavelength correction filter for making correction for wavelengths.

More specifically, this embodiment is structurally different from thefirst embodiment in that a phototaking optical system 101 is provided inits optical path with a wavelength correction filter 103, instead of themeans for reducing color flares, said filter being made up of aplane-parallel plate coated on one side with a film for makingcorrection for wavelengths, thereby decreasing its transmittance withrespect to light rays in the short wavelength range.

For the image pickup optical system 101, use may be made of thoseexplained in the numerical examples of the first and second examples.

It is here noted that the optical elements that take part in thedetermination of a focal length in this image pickup optical system aremade up of those making use of a refraction phenomenon alone.

The spectral transmittance curve for only the optical element in theimage pickup optical system (phototaking optical system 101′) and thespectral transmittance curve for the phototaking optical system pluswavelength correction filter 103 are shown in FIG. 44.

As shown in FIG. 44, the phototaking optical system 101′ plus wavelengthcorrection filter 103 enables the quantity of light on the shortwavelength side—where color flares are likely to occur—to become smalleras compared with the phototaking optical system 101′ alone, so that moresatisfactory images can be obtained.

Specific numerical data about the image pickup optical system accordingto the instant embodiment are now given in the form of Numerical Example3.

NUMERICAL EXAMPLE 3

λc=430 nm

τh=0%

τg=60%

In the electronic image pickup device, g-line sensitivitycharacteristics/e-line sensitivity characteristics=0.35.

In combination with Numerical Example 1:

When (Lλ−Ld)/F_(min)=0.05 mm,

-   -   τ(λ1)=0%    -   τ(λ1+30)=52%

When (Lλ−Ld)/F_(min)=0.04 mm,

-   -   τ(λ1)=0%    -   τ(λ1+30)=62%

When (Lλ−Ld)/F_(min)=0.03 mm,

-   -   τ(λ1)=5%    -   τ(λ1+30)=82%

When |Sλ|=0.025 mm,

-   -   τ(λ2)=0%    -   τ(λ2+30)=50%

When |Sλ|=0.02 mm,

-   -   τ(λ2)=0%    -   τ(λ2+30)=63%

When |Sλ|=0.015 mm,

-   -   τ(λ2)=4%    -   τ(λ2+30)=80%

(Lh−Ld)/F_(min)×τh=0

(Lg−Ld)/F_(min)×τg=0.01133 mm

|Sh|×τh=0

|Sg|×τg=0.00498 mm

In combination with Numerical Example 2:

When (Lλ−Ld)/F_(min)=0.05 mm,

-   -   τ(λ1)=0%    -   (λ1+30)=0%

When (Lλ−Ld)/F_(min)=0.04 mm,

-   -   τ(λ1)=0%    -   τ(λ1+30)=0%

When (Lλ−Ld)/F_(min)=0.03 mm,

-   -   τ(λ1)=0%    -   τ(λ1+30)=0%

When |Sλ|=0.025 mm,

-   -   τ(λ2)=0%    -   τ(λ2+30)=50%

When |Sλ|=0.02 mm,

-   -   τ(λ2)=0%    -   τ(λ2+30)=65%

When |Sλ|=0.015 mm,

-   -   τ(λ2)=5%    -   τ(λ2+30)=82%

(Lh−Ld)/F_(min)×τh=0

(Lg−Ld)/F_(min)×τg=0.004158 mm

|Sh|×τh=0

|Sg|×τg=0.006 mm

The image pickup system according to the instant embodiment may beapplied to an image pickup system different in type from that shown inFIG. 43, for instance, a so-called TTL finder type image pickup systemwherein a light beam is split in front of an electronic image pickupdevice to guide an observation optical path to the eyeball of anobserver and an optical path leading to a finder optical system 126, asshown in FIG. 4. For the image pickup optical system shown in FIG. 45,too, the phototaking optical system explained in each of the aforesaidnumerical examples may be used as the optical system 101. This TTLfinder type is characterized in that the subject can be observed withreduced power consumption. The image pickup system of the type shown inFIG. 45 uses a half-silvered mirror prism 127 as the optical pathsplitter means for the finder optical system 126 and phototaking opticalsystem 101′. The electronic image pickup device or CCD 102 has an imagepickup area where its g-line sensitivity is at least 30% of its e-linesensitivity. On only the optical path on the electronic image pickupdevice side, there is located a low-pass filter 106 having an irregularentrance surface and an exit surface coated with a film 128 for makingthe aforesaid correction for wavelengths.

It is noted that instead of using an infrared cutoff filter, thelow-pass filter 106 may be coated on one side with the aforesaid film.

By carrying out coating in such a way as to ensure the wavelength whosetransmittance becomes a half of the d-line transmittance between g-lineand h-line as well as between 600 nm and 700 nm, the functions ofcutting off infrared rays and reducing color flares are achievable.

Referring to such a triple plate type image pickup device as shown inFIG. 37, the wavelength correction element 3 may be disposed on only anoptical path on the side of a blue image pickup device (B) which has animage pickup area where its g-line sensitivity is 30% or greater of itse-line sensitivity.

FIG. 46 is a schematic of part of another embodiment of the electronicimage pickup system according to the second aspect of the presentinvention. In this embodiment, a turret 129 is disposed on an opticalaxis 105 between an image pickup optical system 101 and an electronicimage pickup device 102 so as to control brightness to 0, −1, −2 and −3levels. Otherwise, the construction of the image pickup optical systemor the like is the same as that of each of the aforesaid embodiments.

The turret 129 is provided thereon with a plane-parallel plate 130, a −1level ND filter 131, −2 level ND filter 132 and −3 level ND filter 133,which are successively positioned on an optical path defined by anoptical axis in unison with the rotation of the turret 129, therebycontrolling the quantity of light incident on the image pickup device102. The plane-parallel plate 130 and ND filters are each provided onits surface with a coating film 128 having a wavelength correctionfunction of allowing its transmittance to become a half-value of itse-line transmittance between g-line and h-line, thereby reducing colorflares due to chromatic aberrations occurring on the shorter wavelengthside. It is noted that the spectral sensitivities of the coating filmsand the optical system are the same as shown in FIG. 44. In associationwith each ND filter, the overall transmittance drops to ½, ¼and ⅛,respectively.

Embodiments of the third aspect of the present invention are nowexplained with reference to the accompanying drawings.

FIG. 47 is a schematic representation of a digital camera that is oneembodiment of the electronic image pickup system according to the thirdaspect of the present invention.

The electronic image pickup system according to the instant embodimentcomprises an electronic image pickup device 201 including a plurality ofpixels having three or more different spectral characteristics so as toobtain a color image and an image pickup optical system 203 for formingthe image of a subject on the image pickup surface 202 of the electronicimage pickup device.

How the image is formed at the center of the image pickup surface 202may be judged on the basis of a spherical aberration diagram. FIG. 48 isa spherical aberration diagram for the image pickup optical system ofFIG. 47 upon focused on an infinite object point. In FIG. 48,Lλrepresents an F-number upon stop in, i.e., the absolute value of adifference between a paraxial image point and the position at theminimum F-number or F_(min) of intersection of the optical axis with amarginal ray of each wavelength with the maximum height of incident rayor, in another parlance, the absolute value of the amount of sphericalaberrations. If λ is d-line (587.56 nm), then the absolute value of theamount of d-line spherical aberrations is represented by Ld, and if λ ish-line (404.7 nm), then the absolute value of the amount of h-linespherical aberrations is represented by Lh.

In the aberration diagram of FIG. 48, Ld and Lh represent the amount ofa focal point displacement at the maximum height of incident ray. FIG.49 is illustrative of how this amount is seen in a sectional view of thevicinity of the center of the image plane of the image pickup opticalsystem in the electronic image pickup system 203 of FIG. 47, i.e., thevicinity of the center of the image pickup surface 202.

In FIG. 49, a solid line indicates a d-line marginal ray at the maximumheight of incident ray and a broken line indicates an h-line marginalray at the maximum height of incident ray. Then, the displacement of theimage plane for each wavelength from the paraxial image plane 202 isperceived in the form of color flares on the paraxial image plane.

In FIG. 49, the amounts (diameter) of displacement of the image planefrom the optical axis 104 on the paraxial image plane 202 are indicatedby Ld/F_(min) and Lh/F_(min), respectively.

A large difference between Ld/F_(min) and Lh/F_(min) makes color flareslikely to occur. To reduce color flares on the side of wavelengthsshorter than d-line, the difference between Ld/F_(min) and Lh/F_(min)should be 0.07 mm or less. That is, it is required to satisfy thefollowing condition (31):(Lh−Ld)/F _(min)≦0.07 mm  (31)

If this condition is satisfied, then it is possible to reduce colorflare-causing color shifts between light beams in the vicinity of h-lineand light beams in the vicinity of d-line, thereby reducing color flareswhile color shifts on the shorter wavelength side can be reduced.

When the difference between Ld/F_(min) and Lh/F_(min) exceeds the upperlimit of 0.07 in condition (31), color flares become striking to theeye.

While the axial chromatic aberrations have so far been explained, it isunderstood that the same also holds for chromatic aberrations ofmagnification. FIG. 50 is an aberration diagram for h-line chromaticaberration of magnification with respect to d-line. In FIG. 50, theamount Sh of h-line transverse chromatic aberration of magnificationwith respect to d-line at image height ratios of 0.9, 0.7 and 0.5 withrespect to the maximum image height IH is indicated by arrows. FIG. 51is illustrative of how chromatic aberrations are produced at the imageheight ratios of 0.9, 0.7 and 0.5 on the paraxial image plane 202 ofFIG. 47. The amount of transverse chromatic aberration of magnificationthat is a chief ray difference between d-line and h-line is perceived inthe form of color flares. To reduce color flares, it is thus required toreduce the amount of shifts at the respective image height ratios to0.04 mm or less or satisfy the following condition (32):|Sh|≦0.04 mm  (32)

When the amount of shifts |Sh| exceeds the upper limit of 0.04 mm incondition (32), color flares becomes striking to the eye becausechromatic aberrations of magnification occur.

According to the instant embodiment, the electronic image pickup systemis constructed in such a way as to satisfy the aforesaid conditions (31)and (32) simultaneously. It is thus possible to reduce color shifts overall the image plane and thereby reproduce a satisfactory image with anunobtrusive color shift even when the subject is of high contrast.

Preferably in the instant embodiment, the upper limit to the aforesaidcondition (31) should be set at 0.05 mm and especially 0.03 mm, becausemore satisfactory images are obtainable.

Preferably in the instant embodiment, the upper limit to the aforesaidcondition (32) should be set at 0.03 mm and especially 0.02 mm, becausemore satisfactory images are obtainable.

The electronic image pickup device 201 is provided with a matrix arrayof pixels. Here the minimum pitch for each pixel is represented by P.Then, the aforesaid condition (31) may be replaced by the followingcondition (33) and the aforesaid condition (32) may be replaced by thefollowing condition (34). In this case, too, it is possible to reducecolor shifts over all the image plane and thereby reproduce asatisfactory image with an unobtrusive color shift even when the subjectis of high contrast.(Lh−Ld)/F _(min)≦6P  (33)|Sh|≦5P  (34)

When (Lh−Ld)/F_(min)>6P or |Sh|>5P, color flares become striking to theeye.

Preferably, the upper limit to the aforesaid condition (33) should beset at 4P and especially 2P, because more satisfactory images areobtainable.

Preferably, the upper limit to the aforesaid condition (34) should beset at 3P and especially 2P, because more satisfactory images areobtainable.

On the other hand, between the pixels of the electronic image pickupdevice 201 there is an area where any light beam cannot be sensed. Thelight sensing efficiency may be increased by the provision ofmicrolenses corresponding to pixels to some degrees, as well known inthe art. However, the area used for light sensing is 40 to 80% withrespect to the image pickup area. For this reason, some chromaticaberrations, if any, have no influence on reproduced images. Inconsideration of influences of overcorrection of each chromaticaberration on other aberrations, it is preferable to satisfy thefollowing conditions (35) and/or (36):(Lh−Ld)/F _(min)≧0.5P  (35)|Sh|≧0.03P  (36)

When the lower limits to the aforesaid conditions (35) and (36) are notreached, there is no influence of chromatic aberrations on reproducedimages. However, it is rather difficult to make correction for otheraberrations.

It is noted that Sh is the amount of transverse chromatic aberration ofmagnification for h-line with respect to d-line at any one of the imageheight ratios of 0.9, 0.7 and 0.5 with respect to the maximum imageheight.

The construction and action of an image pickup optical system suitableto achieve the electronic image pickup system according to the instantembodiment are now explained.

The image pickup optical system 203 shown in FIG. 47 comprises a stop S,and an optical system portion located on the image side with respect tothe stop S comprises three lenses or, in order from its object side, anegative lens, a positive lens and a positive lens.

Preferably in this case, the negative lens should be cemented with thepositive lens on the image side.

It is also preferable that the optical system portion located on theimage side with respect to the stop comprises three lenses or, in orderfrom its object side, a positive lens, a positive lens and a negativelens, optionally with a positive lens group located on the image side ofthe three lenses.

Of the aforesaid positive lenses, the image-side positive lens shouldpreferably be cemented with the aforesaid negative lens.

It is also preferable that the image pickup optical system according tothe instant embodiment should comprise, in order from its object side, afirst group having positive refracting power, a second group havingnegative refracting power, a stop, a third group having positiverefracting power and a fourth group having positive refracting power,with the third group comprising, in order from its object side, one ortwo positive lens and a negative lens.

It is also preferable that the aforesaid third group should comprise adoublet consisting of one positive lens and one negative lens.

It is also preferable that a vitreous material with g- and F-lineanomalous dispersion defined by ΔθgF>0.025 is used for a positivelens(es) in the third and fourth groups, and a vitreous material withanomalous dispersion defined by ΔθgF<0.01 is used for a negativelens(es) therein.

More preferably in this case, the anomalous dispersion of the positivelens should be ΔθgF≧0.027 or the anomalous dispersion of the negativelens should be ΔθgF<0.008.

It is also preferable that the image pickup optical system according tothe instant embodiment should comprise, in order from its object side, afront group comprising a negative meniscus lens convex on its objectside, a stop and a rear group having positive refracting power, with therear group having at least one aspherical surface and at least onepositive lens capable of satisfying the following conditions (37) and(38):ΔθgF(r)>0.025  (37)−0.5<(R1+R2)/(R1−R2)<0.5  (38)where ΔθgF(r) is the anomalous dispersion of a medium of at least onepositive in the rear group, and R1 and R2 are the paraxial radii ofcurvature on the object and image sides of at least one positive lens inthe rear group, respectively.

Generally in the case of a positive lens, the positive value of g-linechromatic aberration of magnification increases drastically withincreasing field angle. The positive value of g-line longitudinalchromatic aberrations is likely to increase, too.

In this type of positive lens in particular, g-line spherical aberrationis likely to assume a plus value, and so flares are likely to occur atwavelengths shorter than d-line.

To prevent both g-line chromatic aberration of magnification and axialchromatic aberration from assuming large plus values, the medium capableof meeting the aforesaid condition (37) should be used for the positivelens located in the rear group and spaced slightly away from the stopand having some axial height of rays.

When the anomalous dispersion of the positive lens medium isΔθgF(r)<0.025, it is difficult to make correction for chromaticaberrations.

For the purpose of correcting chromatic aberrations with the positivelens located in the rear group and spaced slightly away from the stopand having some axial height of rays, it is preferable to use adouble-convex lens which can meet the aforesaid condition (38) and bothsurfaces of which have close radii of curvature, because the angles ofrays are generally small.

When the radii of curvature R1 and R2 of both surfaces exceed the upperlimit to the aforesaid condition (38), color flares of shorterwavelengths are likely to occur.

Preferably in the image pickup optical system according to the instantembodiment, an additional positive lens is incorporated in the reargroup, said positive lens being formed of a medium having a refractiveindex that is at least 0.17 higher than the d-line refractive index ofthe medium of at least one positive lens already used in the rear group.More preferably, the refractive index difference between these positivelenses should be 0.22 or greater.

A medium having a large Abbe number and such large anomalous dispersionas to meet the aforesaid condition (37) often tends to decrease to, say,1.4 to 1.5 in the index of refraction. With such a lens medium, it isdifficult to make correction for spherical aberrations and fieldcurvature. For this reason, it is required to use a lens medium havingsuch a high refractive index as mentioned above for other convex lens inthe rear group.

When the refractive index of the convex lens does not reach the lowerlimit of 0.17, it is difficult to make correction for sphericalaberrations and field curvature.

To make correction for chromatic aberrations with a reduced number oflenses, the rear group should preferably be made up of, in order fromits object side, a doublet component consisting of a negative lens and apositive lens, and a positive lens.

In order to correct various aberrations as well, the front group shouldpreferably be made up of two lenses or, in order from its object side, apositive lens and a negative lens.

In order to make correction for chromatic aberrations with a four-groupzoom lens system, the image pickup optical system should preferablycomprise, in order from its object side, a first group having positiverefracting power, a second group having negative refracting power andmovable for zooming, a stop, a third group having positive refractingpower and a fourth group having positive refracting power and movablefor zooming and focusing, with the four group having at least oneaspherical surface and at least one positive lens capable of satisfyingthe following conditions (39) and (40):ΔθgF(4)>0.025  (39)−0.5<(R14+R24)/(R14−R24)<0.5  (40)where ΔθgF(4) is the anomalous dispersion of a medium of at least onepositive in the rear group, and R14 and R24 are the paraxial radii ofcurvature on the object and image sides of at least one positive lens inthe rear group, respectively.

When the anomalous dispersion of the positive lens medium isΔθgF(4)<0.025, it is difficult to make correction for chromaticaberrations.

When the radii of curvature R14 and R24 of both surfaces exceed theupper limit to the aforesaid condition (40), color flares of shorterwavelengths are likely to occur.

Preferably in the image pickup optical system according to the instantembodiment, an additional positive lens is incorporated in the third orfourth group, said positive lens being formed of a medium having arefractive index that is at least 0.17 higher than the d-line refractiveindex of the medium of at least one positive lens already used in thefourth group.

More preferably, the refractive index difference between these positivelenses should be 0.22 or greater.

It is also preferable that the optical system portion located on theimage side with respect to the stop comprises, in order from its objectside, a positive lens, a doublet component consisting of a positive lensand a negative lens and a positive lens. This is favorable for reducingthe size of the image pickup system and making correction for chromaticaberrations.

Color filters used with the electronic image pickup device positioned inthe vicinity of a subject image in the image pickup system are nowexplained.

To obtain a color image, such a color filter as shown in FIG. 52 or FIG.53 is used with an electronic image pickup device wherein an array ofpixels (photoelectric conversion elements) having three or moredifferent spectral characteristics are arranged at a pitch P.

FIG. 52 is a schematic illustrative of a color filter of the type calleda primary color filter composed of red (R). The primary color filter isconstructed of red (r), green (G) and blue (B) filter elements, therespective wavelength characteristics of which are shown in FIG. 53.

FIG. 54 is a schematic illustrative of a color filter of the type calleda complementary color filter. The complementary color filter isconstructed of cyan (C), magenta (M), yellow (Ye) and green (G) filterelements, the respective characteristics of which are shown in FIG. 55.

The third aspect of the present invention is now explained morespecifically with reference to examples using numerical data.

FIGS. 56(a), 56(b) and 56(c) are sectional views of the lens arrangementof the first example of the electronic image pickup system according tothe third aspect of the present invention, as taken along its opticalaxis, with (a), (b) and (c) illustrating the states of the first exampleat its wide-angle end, its intermediate settings and its telephoto end,respectively. FIGS. 57(a), 57(b) and 57(c) are diagrams illustrative ofspherical aberrations, astigmatism, distortion and chromatic aberrationsfor the first example, with (a), (b) and (c) being aberration diagramsat its wide-angle end, its intermediate settings and its telephoto end,respectively.

The electronic image pickup system according to the first examplecomprises an electronic image pickup device 201 having three or moredifferent spectral characteristics so as to obtain a color image and animage pickup optical system 203 for forming a subject image on the imagepickup surface 202 of the electronic image pickup device.

The image pickup optical system 203 consists of, in order from itsobject side, a first group G1 having positive refractive power, a secondgroup G2 that has negative refracting power and is movable for zooming,a stop S, a third group G3 that has positive refracting power and ismovable for zooming and a fourth group G4 that has positive refractingpower and is movable for zooming and focusing. The third group G3located on the image side with respect to the stop S consists of, inorder from its object side, a positive lens G31, a positive lens G32 anda negative lens G33, with the positive lens G32 and negative lens G33being cemented together.

The fourth group G4 consists of a double-convex lens having anaspherical surface on its object side.

For zooming from the wide-angle end to the telephoto end of the opticalsystem, the second to fourth lens groups G2 to G4 move on the opticalaxis while the first lens group G1 remains fixed. For focusing, thefourth lens group G4 moves on the optical axis.

In FIGS. 56(a) to 56(c), L1, L2 and L3 stand for an optical low-passfilter, an infrared cutoff filter and a cover glass on the electronicimage pickup device 201, respectively.

Set out below are numerical data about the optical elements thatconstitute the electronic image pickup system according to this example.In the following numerical data, ω is the half field angle, r₁, r₂, . .. are the radii of curvature of lens surfaces, d₁, d₂, . . . are thethicknesses or air separations of lenses, ΔθgF₁, ΔθgF₂, . . . are theanomalous dispersion of lens media, n_(d1), n_(d2), . . . are the d-linerefractive indices of lenses, ν₁, ν₂, . . . are the Abbe numbers oflenses, and nh₁, nh₂, . . . are the h-line refractive indices of lenses.

Here let Z represent an optical axis direction and y represent thedirection perpendicular to the optical axis. Then, asphericalconfiguration is given byZ=(y ² /r)/[1+√{1−(1+k)˜(y/r)² }]+AC ₂ y ² AC ₄ y ⁴ +AC ₆ Y ⁶ +AC ₈ y ⁸+AC ₁₀ y ¹⁰ +AC ₁₂ y ¹²where K is the conical coefficient, and AC₂, AC₄, AC₆, AC₈, AC₁₀ andAC₁₂ are the spherical coefficients, respectively.

These symbols are common to the numerical data about the followingexamples. Numerical Data 1 Focal length f = 6.5-10.96-19.5 (mm) F-number2.0-2.3-2.9 Half field angle ω = 33-21-12 (°) r₁ = 39.6531 d₁ = 4.1900ΔθgF₁ = 0.0386 n_(d1) = 1.45600 ν₁ = 90.33 nh₁ = 1.46441 r₂ = −753.3169d₂ = variable r₃ = 22.5664 d₃ = 1.2500 ΔθgF₃ = 0.0174 n_(d3) = 1.84666ν₃ = 23.78 nh₃ = 1.91428 r₄ = 7.9565 d₄ = 5.4000 r₅ = −28.6765 d₅ =1.0000 ΔθgF₅ = −0.0005 n_(d5) = 1.51823 ν₅ = 58.90 nh₅ = 1.53315 r₆ =10.2176 d₆ = 4.5200 ΔθgF₆ = 0.0174 n_(d6) = 1.84666 ν₆ = 23.78 nh₆ =1.91428 r₇ = 52.1549 d₇ = variable r₈ = ∞ (stop) d₈ = variable r₉ =20.6787 (aspheric) d₉ = 3.3600 ΔθgF₉ = 0.0023 n_(d9) = 1.58913 ν₉ =61.25 nh₉ = 1.60531 r₁₀ = −25.0033 d₁₀ = 0.2000 r₁₁ = 9.0354 d₁₁ =4.5000 ΔθgF₁₁ = −0.0096 n_(d11) = 1.74100 ν₁₁ = 52.64 nh₁₁ = 1.76491 r₁₂= 215.0441 d₁₂ = 0.9000 ΔθgF₁₂ = 0.0075 n_(d12) = 1.80518 ν₁₂ = 25.46nh₁₂ = 1.86430 r₁₃ = 6.3536 d₁₃ = variable r₁₄ = 15.4926 (aspheric) d₁₄= 3.2200 ΔθgF₁₄ = 0.0280 n_(d14) = 1.49700 ν₁₄ = 81.54 nh₁₄ = 1.50720r₁₅ = −23.1797 d₁₅ = variable r₁₆ = ∞ d₁₆ = 0.8000 ΔθgF₁₆ = −0.0024n_(d16) = 1.51633 ν₁₆ = 64.14 nh₁₆ = 1.52977 r₁₇ = ∞ d₁₇ = 1.8000 ΔθgF₁₇= −0.0045 n_(d17) = 1.54771 ν₁₇ = 62.84 rh₁₇ = 1.56226 r₁₈ = ∞ d₁₈ =0.8000 r₁₉ = ∞ d₁₉ = 0.7500 ΔθgF₁₉ = −0.0024 n_(d19) = 1.51633 ν₁₉ =64.14 nh₁₉ = 1.52977 r₂₀ = ∞ d₂₀ = variable Electronic image pickupdevice (image plane) ∞ Aspherical surface Ninth surface k = 0. AC2 =0.0000 × 10⁰ AC4 = −6.2681 × 10⁻⁵ AC6 = 2.5583 × 10⁻⁷ AC8 = −3.6774 ×10⁻⁸ AC10 = 1.8093 × 10⁻⁹ AC12 = −2.8329 × 10⁻¹¹ Fourteenth surface k =0 AC2 = 0.0000 × 10⁰ AC4 = −7.6728 × 10⁻⁵ AC6 = −3.6402 × 10⁻⁶ AC8 =6.1375 × 10⁻⁷ AC10 = −3.5417 × 10⁻⁸ AC12 = 7.0508 × 10⁻¹⁰ Zooming dataWide-Angle Intermediate Telephoto d₀ = ∞ ∞ ∞ d₂ = 1.00000 10.9536115.77923 d₇ = 16.29024 6.33662 1.51100 d₈ = 8.57300 6.78687 1.49700 d₁₃= 3.56500 3.36931 5.12785 d₁₅ = 3.16176 5.14358 8.67492 d₂₀ = 1.119461.11936 1.11885 Conditions (37), (38), (39), (40) ΔθgF(r) = ΔθgF(4) =ΔθgF₁₄ = 0.0280 (R1 + R2)/(R1 − R2) = (R14 + R24)/(R14 − R24) = (r₁₄ +r₁₅)/(r₁₄ − r₁₅) = {15.4926 + (−23.1797)}/ {15.4926 − (−23.1797)} ≈−1.9877 d-line Refractive index difference between positive lensesn_(d11) − n_(d14) = 1.74100 − 1.49700 = 0.244 (Lh − Ld)/F_(min)Wide-Angle End Intermediate Telephoto End 0.060919 0.053495 0.059700Amount Sh of transverse chromatic aberrations of magnification forh-line with respect to d-line at image height ratios of 0.9, 0.7 and 0.5with respect to maximum image height Image Height Ratio Wide-Angle EndIntermediate Telephoto End 0.9x 0.010516 (mm) 0.010123 (mm) 0.000658(mm) 0.7x 0.002456 (mm) 0.004998 (mm) 0.000839 (mm) 0.5x 0.001354 (mm)0.002167 (mm) 0.000775 (mm) Pixel pitch P   0.033 (mm)

EXAMPLE 2

FIG. 58 is a schematic illustrative of the lens arrangement of thesecond example of the electronic image pickup system according to thethird aspect of the present invention, as taken along the optical axis,and FIG. 59 is an aberration diagram illustrative of the sphericalaberrations, astigmatism, distortion and chromatic aberrations of thesecond example.

The electronic image pickup system according to this example comprisesan electronic image pickup device 201 including a plurality of pixelshaving three or more spectral characteristics so as to obtain a colorimage, and an image pickup optical system 203 for forming a subjectimage on the image pickup surface 202 of the electronic image pickupdevice.

The image pickup optical system 203 consists of, in order from itsobject side, a first group G1 having positive refracting power, a secondgroup G2 having negative refracting power, a stop S, a third group G3having positive refracting power and a fourth group G4 having positiverefracting power.

The first group G1 consists of one positive lens, and the second groupG2 consists of one negative meniscus lens. The third group G3 located onthe image side of the system with respect to the stop S consists of, inorder from its object side, a negative lens G31 and a positive lens G32which are cemented together. The fourth group G4 consists of adouble-convex lens having an aspherical surface on its object side.

Focusing is carried out by moving the first through fourth lens group G1through G4 on the optical axis while the relative positions thereof arekept.

In FIG. 58, L1, L2 and L3 stand for an optical low-pass filter, aninfrared cutoff filter and a cover glass for the electronic image pickupdevice 201, respectively.

Set out below are numerical data about the optical elements constitutingthe electronic image pickup system according to this example.

Numerical Data 2 Numerical Data 2 Focal length f = 5 (mm) F-number 2.8Half field angle ω = 31 (°) r₁ = 14.3151 d₁ = 2.3000 ΔθgF₁ = 0.0158n_(d1) = 1.80518 ν₁ = 25.42 nh₁ = 1.86494 r₂ = 89.2153 d₂ = 0.2500 r₃ =9.1137 d₃ = 0.7500 ΔθgF₃ = 0.0280 n_(d3) = 1.49700 ν₃ = 81.54 nh₃ =1.50720 r₄ = 2.6148 d₄ = 3.7697 r₅ = ∞ (stop) d₅ = 1.1000 r₆ = −7.9912d₆ = 0.8000 ΔθgF₆ = 0.0075 n_(d6) = 1.80518 ν₆ = 25.46 nh₆ = 1.86430 r₇= 15.0577 d₇ = 3.5000 ΔθgF₇ = −0.0086 n_(d7) = 1.72916 ν₇ = 54.68 nh₇ =1.75173 r₈ = −5.5506 d₈ = 0.1500 r₉ = 9.6764 (aspheric) d₉ = 3.6000ΔθgF₉ = 0.0280 n_(d9) = 1.49700 ν₉ = 81.54 nh₉ = 1.50720 r₁₀ = −8.2960d₁₀ = 1.5000 r₁₁ = ∞ d₁₁ = 1.6000 ΔθgF₁₁ = −0.0024 n_(d11) = 1.51633 ν₁₁= 64.15 nh₁₁ = 1.52977 r₁₂ = ∞ d₁₂ = 2.0200 ΔθgF₁₂ = −0.0024 n_(d12) =1.51633 ν₁₂ = 64.15 nh₁₂ = 1.52977 r₁₃ = ∞ d₁₃ = 1.6000 r₁₄ = ∞ d₁₄ =0.7500 ΔθgF₁₄ = 0.0022 n_(d14) = 1.48749 ν₁₄ = 70.21 nh₁₄ = 1.49898 r₁₅= ∞ d₁₅ = 1.1866 Electronic image pickup device (image plane) ∞Aspherical surface Ninth surface k = 0 AC2 = 0.0000 × 10⁰ AC4 = −7.1869× 10⁻⁴ AC6 = −1.4974 × 10⁻⁵ AC8 = 1.8101 × 10⁻⁶ AC10 = −7.6598 × 10⁻⁸Conditions (37), (38) ΔθgF(r) = ΔθgF₉ = 0.0280 (R1 + R2)/(R1 − R2) =(r₉ + r₁₀)/(r₉ − r₁₀) = {9.6764 + (−8.2960)}/ {9.6764 − (−8.2960)} ≈−0.07681 d-line Refractive index difference between positive lensesn_(d7) − n_(d9) = 1.72916 − 1.49700 = 0.232 (Lh − Ld)/F_(min) 0.024384(mm) Wide-Angle End Intermediate Telephoto End 0.060919 0.0534950.059700 Amount Sh of transverse chromatic aberrations of magnificationfor h-line with respect to d-line at image height ratios of 0.9, 0.7 and0.5 with respect to maximum image height Image height ratio Sh 0.9x0.017038 (mm) 0.7x 0.000308 (mm) 0.5x 0.004529 (mm) Pixel pitch P  0.033 (mm)

Embodiments and examples of the image pickup system according to thefourth aspect of the present invention are now explained with referenceto the accompanying drawings.

FIG. 60 is a schematic illustrative of a so-called digital camera 310. Alight beam emanating from an object point is subjected to imageformation by a phototaking lens system 301 made up of an optical elementto form an image on an image pickup device 303 such as a CCD. To preventa so-called moire phenomenon resulting from the fact that the imagepickup device 303 is an array of regularly located photoelectricconverters, a filter 302 having a low-pass effect is located on theobject side of the system with respect to the image pickup surface 303.In addition, a filter having an IR cutoff effect for cutting offinfrared light may be located. The light beam incident on the imagepickup element 303 is converted by the photoelectric converters toelectric signals, which are then entered into a controller 304. Theelectric signals are subjected at the controller 4 to signal processingsuch as gamma correction or image compression processing, and sent via abuilt-in memory 305 and an interface 307 to a personal computer 308 orthe like. The resulting signals may be transmitted from the controller304 to a liquid crystal monitor 306 which makes it possible for theoperator to check up the image to be phototaken or the phototaken image.Alternatively, image data may be transmitted from the built-in memory 5to an auxiliary memory 309 such as a so-called smart medium (trademark).

In this embodiment, d represents the diagonal length of an effectiveimage pickup area of the image pickup device 303 and p represents thecenter separation between horizontal pixels. Then, the image pickupdevice should satisfy the following condition (41), and has acomplementary color filter comprising at least four color filterelements.1.0×10⁻⁴ <p/d<6.0×10⁻⁴  (41)

The combined transmittance of the image pickup lens system 301 andfilter 302 should satisfy the following conditions (42) and (43):8×T ₇₀₀ <T ₆₀₀  (42)T₄₀₀<T₆₀₀  (43)Here T₄₀₀ is the 400-nm transmittance, T₆₀₀ is the 600-nm transmittanceand T₇₀₀ is the 700-nm transmittance.

Alternatively, the output signals from the image pickup device 303 havethe following characteristics. That is, the system is designed in such away that the spectral strength curve for output signals from at leastone color filter (which curve is obtained by plotting the strengths ofoutput signals of each wavelength when light is incident on thephototaking optical system with uniform strength for each wavelength)satisfies the following condition (44):0.45<(S ₆₀₀ −S ₆₅₀)/Sp<0.85  (44)where Sp is the spectral strength peak, S₆₀₀ is the strength of 600 nmand S₆₅₀ is the strength of 650 nm.

The image pickup device 303 is provided with a color filter at suchsettings as shown in FIG. 62. This color filter is a filter of the typecalled a complementary color mosaic filter comprising cyan (C), magenta(M), yellow (Ye) and green (G) filter elements, each used in much thesame number. One example of the wavelength characteristics of eachfilter element is shown in FIG. 64. When the complementary color filteris used as the filter, the filtered light is converted by the controller304 to R, G and B according to the following processing:

for luminance signalsY=|G+M+Ye+C|*¼for color signalsR−Y═|(M+Ye)−(G+C)|B−Y═|(M+C)−(G+Ye)|With the complementary color filter, it is possible to increase thequantity of light with respect to the photoelectric conversion surfaces.

Alternatively, the filter 302 may be coated by evaporation with a thinfilm having such spectral characteristics as shown in FIG. 65 and havingan infrared cutoff function. FIG. 66 is illustrative of the combinedcharacteristics of a standard light source D₆₅ having such spectralcharacteristics as shown in FIG. 71, the phototaking lens system 301having such a transmittance as shown in FIG. 72, the infrared cutofffilter shown in FIG. 65 and the complementary color filter shown in FIG.62. Signal strength profiles for the development of R, G and Bcalculated from FIG. 66 are shown in FIG. 67. For reference, one exampleof the characteristics of a commonly used absorption type infraredcutoff filter is shown in FIG. 68. The combined characteristics of thecharacteristics of the standard light source D₆₅ and phototaking lenssystem 301 and the characteristics of the infrared filter andcomplementary color filter when used in combination with such aninfrared cutoff filter are shown in FIG. 69. Signal strength profilesfor the development of R, G and B calculated from FIG. 69 are shown inFIG. 70.

From a comparison of FIG. 67 with FIG. 70, it is found that the strengthof R signals in the vicinity of 430 nm in particular becomes weak whilethe strength thereof in the vicinity of 620 nm becomes strong. It isalso found that the strength of B signals in the vicinity of 450 nmbecomes strong. In other words, red can be seen just as red and bluejust as blue. Flares occurring due to chromatic aberrations on theshorter wavelength side have inherently low energy. In addition, theflares have only a limited influence on the development of striking red,and so have a primary action on the development of relativelyunobtrusive blue. In other words, the flare information on the shorterwavelength side has no particularly great influence on a substantialscreen carrying a large amount of information.

FIG. 73 shows a modification to the FIG. 60 embodiment, using aso-called TTL finder type wherein a light beam is split by ahalf-silvered mirror prism 312 located on the object side of the imagepickup element 303 for guidance to a finder optical system 313. Thistype is characterized in that a subject can be observed with reducedpower consumption. The present invention may also be applied to such atype.

It is noted that the infrared cutoff function according to the presentinvention may be added to the characteristics of the complementaryfilter itself.

In another embodiment, a phototaking lens system 301 may be detachablefrom a body including an image pickup device 303 as shown in FIG. 74. Amount 15 used to this end, for instance, may be of either the screwcoupling type or the bayonet coupling type. In this case, the infraredcutoff function according to the present invention may be imparted tothe phototaking lens system 301 or to the body including image pickupdevice 303.

It is understood that the image pickup system according to the presentinvention may be used to not only digital cameras but also to cellularphones equipped with an image pickup device, a notebook type of PCs,etc.

Set out below are Examples A′ through G′ of the optical system suitablefor use with the aforesaid embodiments of the present invention. Someexamples use filters and some do not; the filters may be optionallyused.

FIGS. 75 to 77 are sectional views of Examples A′ to C′, each includingan optical axis. Likewise, FIGS. 78 to 81 are sectional views ofExamples D′ to G′, each including an optical axis at a wide-angle end.Examples A′ to C′ are each directed to a lens system having a fixedfocal length while Examples D′ to G′ are each directed to a zoom lenssystem having a variable focal length. In each figure, F denotes filtersand prisms, and I stands for an image plane. Example B′ is suitable forslimming down a camera because a reflecting member R is located withinan image pickup optical system. Alternatively, the reflectingcharacteristics of this reflecting member R may be used instead of theinfrared cutoff function according to the present invention. Example D′is suitable for use with the so-called TTL finder type.

The lens arrangement of each example is now explained.

The lens system of Example A′ consists of four groups or five lenses,i.e., a positive meniscus lens convex on its object side, a negativemeniscus lens convex on its object side, a stop, a doublet composed of adouble-concave lens and a double-convex lens and a double convex lens,as shown in FIG. 75. One aspherical surface is used at the object-sidesurface of the double-convex lens located nearest to the image planeside of the system.

The lens system of Example B′ consists of four groups or five lenses,i.e., a negative meniscus lens convex on its object side, a reflectingsurface R for turning back an optical path, a stop, a double-convexlens, a doublet composed of a double-convex lens and a double-concavelens and a positive lens having a strong convex surface on its imageside, as shown in FIG. 76. Two aspherical surfaces are used, one at thesurface of the double-convex lens located in the rear of the stop andanother at the surface of the positive lens located nearest to the imageplane side of the system.

The system of Example C′ consists of five groups or six lenses, i.e.,two negative meniscus lenses, each convex on its object side, a convexlens, a stop, a doublet composed of a double-concave lens and adouble-convex lens, and a double-convex lens, as shown in FIG. 77. Twoaspherical surfaces are used, one at the surface of the second negativemeniscus lens and another at the surface of the double-convex lenslocated nearest to the image plane side of the system. The system ofExample D′ consists of four groups G1 to G4. As shown in FIG. 78, thefirst group G1 consists of three lenses or a doublet composed of anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side and a positive meniscus lens convex onits object side, the second group G2 consists of four lenses or anegative meniscus lens convex on its object side, a double-concave lensand a doublet composed of a double-concave lens and a positive meniscuslens convex on its object side, in the rear of which a stop S islocated, the third group G3 consists of three lenses or a positivemeniscus lens convex on its object side, a double-convex lens and anegative meniscus lens convex on its object side, and the fourth groupG4 consists of four lenses or a doublet composed of a negative meniscuslens convex on its image plane side and a positive meniscus lens convexon its image plane side and two double-convex lenses. Two asphericalsurfaces are used, one at the object-side surface of the double-convexlens in the third group G3 and another at the surface of the lens in thefourth group G4, which is located nearest to the image plane side of thesystem. For zooming from the wide-angle end to the telephoto end of thesystem, the second group G2 moves from the object side to the imageplane side and the third and fourth groups G3 and G4 move from the imageplane side to the object side, as indicated by arrows, while the firstgroup G1 and stop S remain fixed.

The system of Example E′ consists of four lens groups G1 to G4. As shownin FIG. 79, the first group G1 consists of one convex lens, the secondgroup G2 consists of a negative meniscus lens convex on its object sideand a doublet composed of a double-concave lens and a positive meniscuslens convex on its object side, in the rear of which a stop S islocated, the third group G3 consists of a double-convex lens and adoublet composed of a positive meniscus lens convex on its object sideand a negative meniscus lens convex on its object side, and the fourthgroup G4 consists of one double-convex lens. Two aspherical surfaces areused, one at the surface of the lens in the third group G3, which islocated nearest to the object side of the system, and another at thesurface of the lens in the fourth group G4, which is located nearest tothe object side of the system. For zooming from the wide-angle end tothe telephoto end of the system, the second group G2 moves from theobject side to the image plane side and the third and fourth groups G3and G4 move from the image plane side to the object side with theseparation between them becoming wide, as indicated by arrows, while thefirst group G1 and stop S remain fixed.

The system of Example F′ consists of four groups G1 to G4. As shown inFIG. 80, the first group G1 consists of one positive lens convex on itsobject side, the second group G2 consists of a negative meniscus lensconvex on its object side, a double-concave lens and a positive lenshaving a strong convex surface on its object side, in the rear of whichthere is a stop S, the third group G3 consists of a double-convex lensand a negative meniscus lens convex on its object side, and the fourthgroup G4 consists of one positive lens having a strong convex surface onits image plane side. One aspherical surface is used at the object-sidesurface of the positive lens in the fourth group G4. For zooming fromthe wide-angle end to the telephoto end of the system, the second groupG2 moves from the object side to the image plane side and the third andfourth groups G3 and G4 move from the image plane side to the objectside, as indicated by arrows, while the first group G1 and stop S remainfixed.

The system of Example G′ consists of three groups G1 to G3. As shown inFIG. 81, the first group G1 consists of two negative meniscus lenses,each convex on its object side, and a positive meniscus lens having astrong convex surface on its object side, the second group G2 consistsof a double-convex lens and a doublet composed of a positive meniscuslens having a strong convex surface on its object side and a negativemeniscus lens having a strong concave surface on its image side, and thethird group G3 consists of a positive meniscus lens having a strongconvex surface on its image side. Two aspherical surfaces are used, oneat the surface located nearest to the object side in the second group G2and another at the image side-surface of the single lens in the thirdgroup G3. For zooming from the wide-angle end to the telephoto end ofthe system, the first group G1 first moves to the image side and thenmoves to the object side in a convex orbit while the third group G3remains fixed, and the second group G2 moves together with the stop Sfrom the image side to the object side, as indicated by arrows.

Enumerated below are numerical data about each example. The symbols usedhereinafter but not referred to hereinbefore have the followingmeanings.

FNO: F-number,

2ω: field angle (an effective diagonal field angle),

p: pixel pitch,

r₁, r₂, . . . : radius of curvature of each lens surface,

d₁, d₂, . . . : separation between adjacent lenses,

n_(d1), n_(d2), . . . : d-line refractive index of each lens,

n_(g1), n_(g2), . . . : g-line refractive index of each lens,

n_(h1), n_(h2), . . . : h-line refractive index of each lens,

Δθ_(RN1), Δθ_(RN2), . . . : value of ΔθRN of each lens, and

ν_(d1), ν_(d2), . . . : d-line Abbe number of each lens.

The radii of curvature and separations are given by the mm unit. Herelet x represent an optical axis provided that the direction ofpropagation of light is defined as positive and y represent thedirection perpendicular to the optical axis. Then, asphericalconfiguration is given byx=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ Y ⁶ +A ₈ Y ⁸ +A ₁₀ Y¹⁰ +A ₁₂ y ¹²where r is the paraxial radius of curvature, K is the conicalcoefficient, and A₄, A₆, A₈, A₁₀ and A₁₂ are the fourth, sixth, eighth,tenth and twelfth spherical coefficients, respectively.

EXAMPLE A′

f = 5.55 mm F_(NO) = 2.88 2ω = 64.4° p = 3.8 μm d = 6.64 mm r₁ = 13.9598d₁ = 2.4200 n_(d1) = 1.84666 ν_(d1) = 23.78 r₂ = 56.3701 d₂ = 0.2700 r₃= 7.6185 d₃ = 0.8700 n_(d2) = 1.48749 ν_(d2) = 70.21 r₄ = 2.4917 d₄ =3.3154 r₅ = ∞ (Stop) d₅ = 1.0735 r₆ = −8.2879 d₆ = 0.8000 n_(d3) =1.84666 ν_(d3) = 23.78 r₇ = 10.5000 d₇ = 3.7900 n_(d4) = 1.72916 ν_(d4)= 54.68 r₈ = −5.2842 d₈ = 0.1500 r₉ = 9.8776 (Aspheric) d₉ = 3.3700n_(d5) = 1.56384 ν_(d5) = 60.67 r₁₀ = −13.3796 d₁₀ = 2.7100 r₁₁ = ∞ d₁₁= 2.3200 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₂ = ∞ d₁₂ = 1.6000 r₁₃ = ∞d₁₃ = 0.8000 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₄ = ∞ d₁₄ = 1.0048 r₁₅ =∞ (Image plane) n_(g1) = 1.89419 n_(h1) = 1.91428 Δθ_(RN1) = +0.0174n_(g2) = 1.49596 n_(h2) = 1.49898 Δθ_(RN2) = +0.0022 n_(g3) = 1.89419n_(h3) = 1.91428 Δθ_(RN3) = +0.0174 n_(g4) = 1.74570 n_(h4) = 1.75173Δθ_(RN4) = −0.0086 n_(g5) = 1.57532 n_(h5) = 1.57947 Δθ_(RN5) = −0.0031n_(g6) = 1.52621 n_(h6) = 1.52977 Δθ_(RN6) = −0.0024 n_(g7) = 1.52621n_(h7) = 1.52977 Δθ_(RN7) = −0.0024 Aspherical Coefficients 9th surfaceK = 0 A₄ = −3.6930 × 10⁻⁴ A₆ = 7.0898 × 10⁻⁷

EXAMPLE B′

f = 9.88 F_(NO) = 2.8 2ω = 59.12° p = 3.9 μm d = 11 r₁ = 42.746 d₁ =1.80 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = 9.841 d₂ = 21.36 r₃ = ∞ (Stop)d₃ = 5.09 r₄ = 96.670 d₄ = 4.16 n_(d2) = 1.69350 ν_(d2) = 53.20 r₅ =−14.943 d₅ = 0.08 (Aspheric) r₆ = 9.051 d₆ = 6.95 n_(d3) = 1.62041ν_(d3) = 60.29 r₇ = −33.014 d₇ = 0.98 n_(d4) = 1.80518 ν_(d4) = 25.42 r₈= 5.859 d₈ = 4.21 r₉ = −51.618 d₉ = 5.06 n_(d5) = 1.58913 ν_(d5) = 61.28r₁₀ = −7.361 d₁₀ = 1.50 (Aspheric) r₁₁ = ∞ d₁₁ = 1.00 n_(d6) = 1.51633ν_(d6) = 64.14 r₁₂ = ∞ d₁₂ = 1.60 n_(d7) = 1.54771 ν_(d7) = 62.84 r₁₃ =∞ n_(g1) = 1.49596 n_(h1) = 1.49898 Δθ_(RN1) = +0.0022 n_(g2) = 1.70972n_(h2) = 1.71566 Δθ_(RN2) = −0.0081 n_(g3) = 1.63315 n_(h3) = 1.63778Δθ_(RN3) = −0.0012 n_(g4) = 1.84729 n_(h4) = 1.86494 Δθ_(RN4) = +0.0158n_(g5) = 1.60103 n_(h5) = 1.60535 Δθ_(RN5) = −0.0018 n_(g6) = 1.52621n_(h6) = 1.52977 Δθ_(RN6) = −0.0024 n_(g7) = 1.55843 n_(h7) = 1.56226Δθ_(RN7) = −0.0045 Aspherical Coefficients 5th surface K = 0 A₄ =6.18542 × 10⁻⁵ A₆ = 3.07784 × 10⁻⁷ 10th surface K = 0 A₄ = 4.92151 ×10⁻⁴ A₆ = −3.57904 × 10⁻⁶ A₈ = 4.22919 × 10⁻⁸

EXAMPLE C′

f = 4.4182 F_(NO) = 2.4 2ω = 80.9° p = 3.8 μm or 3 μm d = 6.64 r₁ =13.2550 d₁ = 0.9000 n_(d1) = 1.60311 ν_(d1) = 60.64 r₂ = 7.0317 d₂ =1.0000 r₃ = 12.0000 (Aspheric) d₃ = 0.8000 n_(d2) = 1.56384 ν_(d2) =60.67 r₄ = 4.9103 d₄ = 4.6372 r₅ = 7.9159 d₅ = 1.1424 n_(d3) = 1.84666ν_(d3) = 23.78 r₆ = ∞ d₆ = 0.5000 r₇ = ∞ (Stop) d₇ = 1.8751 r₈ = −3.7652d₈ = 1.0000 n_(d4) = 1.80518 ν_(d4) = 25.42 r₉ = 8.7546 d₉ = 2.1667n_(d5) = 1.72916 ν_(d5) = 54.68 r₁₀ = −4.8805 d₁₀ = 0.1500 r₁₁ = 10.0186d₁₁ = 2.2298 n_(d6) = 1.56384 ν_(d6) = 60.67 (Aspheric) r₁₂ = −8.4667d₁₂ = 2.3588 r₁₃ = ∞ d₁₃ = 1.9000 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₄ =∞ d₁₄ = 0.8000 n_(d8) = 1.51633 ν_(d8) = 64.14 r₁₅ = ∞ d₁₅ = 1.2000 r₁₆= ∞ d₁₆ = 0.7500 n_(d9) = 1.48749 ν_(d9) = 70.23 r₁₇ = ∞ d₁₇ = 1.2200r₁₈ = ∞ (Image plane) n_(g1) = 1.61541 n_(h1) = 1.61987 Δθ_(RN1) =−0.0019 n_(g2) = 1.57532 n_(h2) = 1.57947 Δθ_(RN2) = −0.0031 n_(g3) =1.89419 n_(h3) = 1.91428 Δθ_(RN3) = +0.0174 n_(g4) = 1.84729 n_(h4) =1.86494 Δθ_(RN4) = +0.0158 n_(g5) = 1.74570 n_(h5) = 1.75173 Δθ_(RN5) =−0.0086 n_(g6) = 1.57532 n_(h6) = 1.57947 Δθ_(RN6) = −0.0031 n_(g7) =1.52621 n_(h7) = 1.52977 Δθ_(RN7) = −0.0024 n_(g8) = 1.52621 n_(h8) =1.52977 Δθ_(RN8) = −0.0024 n_(g9) = 1.49596 n_(h9) = 1.49898 Δθ_(RN9) =+0.0022 Aspherical Coefficients 3rd surface K = 0 A₄ = 3.1698 × 10⁻⁴ A₆= 6.1083 × 10⁻⁵ A₈ = −4.6332 × 10⁻⁶ A₁₀ = −1.4286 × 10⁻⁷ 11th surface K= 0 A₄ = −1.0432 × 10⁻³ A₆ = −2.9351 × 10⁻⁵ A₈ = 4.2352 × 10⁻⁶ A₁₀ =−1.8071 × 10⁻⁷

EXAMPLE D′

f = 9.099˜18.100˜35.998 F_(NO) = 2.008˜2.065˜2.481 2ω =68.4°˜35.8°˜18.6° p = 3.5 μm d = 11 r₁ = 74.1213 d₁ = 2.5000 n_(d1) =1.84666 ν_(d1) = 23.78 r₂ = 45.2920 d₂ = 7.6976 n_(d2) = 1.61800 ν_(d2)= 63.33 r₃ = 200.0000 d₃ = 0.1500 r₄ = 53.6322 d₄ = 5.1636 n_(d3) =1.77250 ν_(d3) = 49.60 r₅ = 160.3763 d₅ = (Variable) r₆ = 86.4469 d₆ =1.8938 n_(d4) = 1.77250 ν_(d4) = 49.60 r₇ = 12.9947 d₇ = 6.5582 r₈ =−633.9388 d₈ = 1.3849 n_(d5) = 1.84666 ν_(d5) = 23.78 r₉ = 53.5036 d₉ =3.0086 r₁₀ = −70.1852 d₁₀ = 1.3000 n_(d6) = 1.48749 ν_(d6) = 70.21 r₁₁ =19.4251 d₁₁ = 4.0971 n_(d7) = 1.80518 ν_(d7) = 25.42 r₁₂ = 567.6091 d₁₂= (Variable) r₁₃ = ∞ (Stop) d₁₃ = (Variable) r₁₄ = 35.5332 d₁₄ = 2.9155n_(d8) = 1.84666 ν_(d8) = 23.78 r₁₅ = 149.5334 d₁₅ = 1.9951 r₁₆ =23.1874 d₁₆ = 3.2540 n_(d9) = 1.69350 ν_(d9) = 53.20 (Aspheric) r₁₇ =−136.5790 d₁₇ = 0.1500 r₁₈ = 54.2006 d₁₈ = 1.1258 n_(d10) = 1.80518ν_(d10) = 25.42 r₁₉ = 17.2110 d₁₉ = (Variable) r₂₀ = −12.6096 d₂₀ =1.1000 n_(d11) = 1.80518 ν_(d11) = 25.42 r₂₁ = −55.3792 d₂₁ = 3.1600n_(d12) = 1.61800 ν_(d12) = 63.33 r₂₂ = −15.6001 d₂₂ = 0.1500 r₂₃ =74.9447 d₂₃ = 3.2661 n_(d13) = 1.61800 ν_(d13) = 63.33 r₂₄ = −30.4739d₂₄ = 0.1500 r₂₅ = 124.0475 d₂₅ = 2.5117 n_(d14) = 1.69350 ν_(d14) =53.20 r₂₆ = −68.0400 d₂₆ = (Aspheric) (Variable) r₂₇ = ∞ d₂₇ = 24.0000n_(d15) = 1.51633 ν_(d15) = 64.14 r₂₈ = ∞ d₂₈ = 1.0000 r₂₉ = ∞ d₂₉ =1.5700 n_(d16) = 1.54771 ν_(d16) = 62.84 r₃₀ = ∞ d₃₀ = 1.0000 r₃₁ = ∞d₃₁ = 0.8000 n_(d17) = 1.51823 ν_(d17) = 58.96 r₃₂ = ∞ n_(g1) = 1.89419n_(h1) = 1.91428 Δθ_(RN1) = +0.0174 n_(g2) = 1.63010 n_(h2) = 1.63451Δθ_(RN2) = +0.0051 n_(g3) = 1.79197 n_(h3) = 1.79917 Δθ_(RN3) = −0.0092n_(g4) = 1.79197 n_(h4) = 1.79917 Δθ_(RN4) = −0.0092 n_(g5) = 1.89419n_(h5) = 1.91428 Δθ_(RN5) = +0.0174 n_(g6) = 1.49596 n_(h6) = 1.49898Δθ_(RN6) = +0.0022 n_(g7) = 1.84729 n_(h7) = 1.86494 Δθ_(RN7) = +0.0158n_(g8) = 1.89419 n_(h8) = 1.91428 Δθ_(RN8) = +0.0174 n_(g9) = 1.70972n_(h9) = 1.71566 Δθ_(RN9) = −0.0081 n_(g10) = 1.84729 n_(h10) = 1.86494Δθ_(RN10) = +0.0158 n_(g11) = 1.84729 n_(h11) = 1.86494 Δθ_(RN11) =+0.0158 n_(g12) = 1.63010 n_(h12) = 1.63451 Δθ_(RN12) = +0.0051 n_(g13)= 1.63010 n_(h13) = 1.63451 Δθ_(RN13) = +0.0051 n_(g14) = 1.70972n_(h14) = 1.71566 Δθ_(RN14) = −0.0081 n_(g15) = 1.52621 n_(h15) =1.52977 Δθ_(RN15) = −0.0024 n_(g16) = 1.55843 n_(h16) = 1.56226Δθ_(RN16) = −0.0045 n_(g17) = 1.52915 n_(h17) = 1.53314 Δθ_(RN17) =+0.0035 Zooming Spaces f 9.099 18.100 35.998 d₅ 1.006 18.105 28.360 d₁₂28.950 11.850 1.597 d₁₃ 12.005 9.317 1.499 d₁₉ 7.213 7.088 10.629 d₂₆1.500 4.313 8.589 Aspherical Coefficients 16th surface K = 0 A₄ =−1.3659 × 10⁻⁵ A₆ = −5.3156 × 10⁻⁹ A₈ = −2.4548 × 10⁻¹¹ A₁₀ = 2.2544 ×10⁻¹² 26th surface K = 0 A₄ = 6.6763 × 10⁻⁶ A₆ = 3.7977 × 10⁻⁸ A₈ =−4.9995 × 10⁻¹⁰ A₁₀ = 2.3437 × 10⁻¹²

EXAMPLE E′

f = 6.608˜11.270˜19.098 F_(NO) = 2.03˜2.36˜2.91 p = 3.9 μm or 3.2 μm d =8 r₁ = 36.688 d₁ = 4.14 n_(d1) = 1.48749 ν_(d1) = 70.23 r₂ = ∞ d₂ =(Variable) r₃ = 21.750 d₃ = 1.25 n_(d2) = 1.84666 ν_(d2) = 23.78 r₄ =8.054 d₄ = 5.45 r₅ = −27.511 d₅ = 1.00 n_(d3) = 1.48749 ν_(d3) = 70.23r₆ = 10.412 d₆ = 4.50 n_(d4) = 1.84666 ν_(d4) = 23.78 r₇ = 40.550 d₇ =(Variable) r₈ = ∞ (Stop) d₈ = (Variable) r₉ = 17.583 (Aspheric) d₉ =3.42 n_(d5) = 1.58913 ν_(d5) = 61.30 r₁₀ = −35.670 d₁₀ = 0.20 r₁₁ =9.390 d₁₁ = 4.35 n_(d6) = 1.77250 ν_(d6) = 49.60 r₁₂ = 87.943 d₁₂ = 0.90n_(d7) = 1.84666 ν_(d7) = 23.78 r₁₃ = 6.609 d₁₃ = (Variable) r₁₄ =13.553 (Aspheric) d₁₄ = 3.28 n_(d8) = 1.58913 ν_(d8) = 61.30 r₁₅ =−30.808 n_(g1) = 1.49596 n_(h1) = 1.49898 Δθ_(RN1) = +0.0022 n_(g2) =1.89419 n_(h2) = 1.91428 Δθ_(RN2) = +0.0174 n_(g3) = 1.49596 n_(h3) =1.49898 Δθ_(RN3) = +0.0022 n_(g4) = 1.89419 n_(h4) = 1.91428 Δθ_(RN4) =+0.0174 n_(g5) = 1.60103 n_(h5) = 1.60535 Δθ_(RN5) = −0.0018 n_(g6) =1.79197 n_(h6) = 1.79917 Δθ_(RN6) = −0.0092 n_(g7) = 1.89419 n_(h7) =1.91428 Δθ_(RN7) = +0.0174 n_(g8) = 1.60103 n_(h8) = 1.60535 Δθ_(RN8) =−0.0018 Zooming Spaces f 6.608 11.270 19.098 d₂ 1.00 9.66 15.80 d₇ 16.207.55 1.50 d₈ 8.66 5.46 1.50 d₁₃ 3.46 5.00 5.71 Aspherical Coefficients9th surface K = 0.000 A₄ = −4.66054 × 10⁻⁵ A₆ = −1.33346 × 10⁻⁶ A₈ =6.88261 × 10⁻⁸ A₁₀ = −1.18171 × 10⁻⁹ A₁₂ = 1.21868 × 10⁻¹² 14th surfaceK = 0.000 A₄ = −9.93375 × 10⁻⁵ A₆ = −9.76311 × 10⁻⁷ A₈ = 3.21037 × 10⁻⁷A₁₀ = −1.95172 × 10⁻⁸ A₁₂ = 3.74139 × 10⁻¹⁰

EXAMPLE F′

f = 9.000˜15.590˜27.000 F_(NO) = 2.800˜3.030˜4.069 2ω =67.094°˜39.462°˜23.030° p = 6.7 μm or 4 μm d = 11 r₁ = 44.5137 d₁ =4.4000 n_(d1) = 1.69680 ν_(d1) = 55.53 r₂ = 137.7320 d₂ = (Variable) r₃= 23.5602 d₃ = 1.6000 n_(d2) = 1.69680 ν_(d2) = 55.53 r₄ = 12.0406 d₄ =5.7412 r₅ = −54.8255 d₅ = 1.5000 n_(d3) = 1.56384 ν_(d3) = 60.70 r₆ =13.6238 d₆ = 3.8135 r₇ = 16.0196 d₇ = 2.2000 n_(d4) = 1.84666 ν_(d4) =23.78 r₈ = 23.3091 d₈ = (Variable) r₉ = ∞ (Stop) d₉ = (Variable) r₁₀ =31.1300 d₁₀ = 6.5179 n_(d5) = 1.77250 ν_(d5) = 49.60 r₁₁ = −15.0403 d₁₁= 0.1939 r₁₂ = −13.3787 d₁₂ = 0.8893 n_(d6) = 1.84666 ν_(d6) = 23.78 r₁₃= −65.0570 (Variable) d₁₃ = r₁₄ = −2370.3961 d₁₄ = 4.3000 n_(d7) =1.49241 ν_(d7) = 57.66 (Aspheric) r₁₅ = −14.2694 d₁₅ = (Variable) r₁₆ =∞ d₁₆ = 1.1400 n_(d8) = 1.54771 ν_(d8) = 62.84 r₁₇ = ∞ d₁₇ = 0.8100n_(d9) = 1.54771 ν_(d9) = 62.84 r₁₈ = ∞ d₁₈ = 1.0000 r₁₉ = ∞ d₁₉ =1.0000 n_(d10) = 1.48749 ν_(d10) = 70.23 r₂₀ = ∞ d₂₀ = 1.0000 r₂₁ = ∞d₂₁ = 0.8000 n_(d11) = 1.51823 ν_(d11) = 58.96 r₂₂ = ∞ n_(g1) = 1.71234n_(h1) = 1.71800 Δθ_(RN1) = −0.0082 n_(g2) = 1.71234 n_(h2) = 1.71800Δθ_(RN2) = −0.0082 n_(g3) = 1.57532 n_(h3) = 1.57947 Δθ_(RN3) = −0.0031n_(g4) = 1.89419 n_(h4) = 1.91428 Δθ_(RN4) = +0.0174 n_(g5) = 1.79197n_(h5) = 1.79917 Δθ_(RN5) = −0.0092 n_(g6) = 1.89419 n_(h6) = 1.91428Δθ_(RN6) = +0.0174 n_(g7) = 1.50320 n_(h7) = 1.50713 Δθ_(RN7) = +0.0104n_(g8) = 1.55843 n_(h8) = 1.56226 Δθ_(RN8) = −0.0045 n_(g9) = 1.55843n_(h9) = 1.56226 Δθ_(RN9) = −0.0045 n_(g10) = 1.49596 n_(h10) = 1.49898Δθ_(RN10) = +0.0022 n_(g11) = 1.52915 n_(h11) = 1.53314 Δθ_(RN11) =+0.0035 Zooming Spaces f 9.000 15.590 27.000 d₂ 1.000 13.349 18.974 d₈20.474 8.125 2.500 d₉ 13.221 9.796 2.000 d₁₃ 6.416 6.356 7.516 d₁₅15.209 18.694 25.330 Aspherical Coefficients 14th surface K = 0.0000 A₄= −7.8946 × 10⁻⁵ A₆ = 3.2441 × 10⁻⁸ A₈ = −1.6090 × 10⁻⁹ A₁₀ = 1.6631 ×10⁻¹¹

EXAMPLE G′

f = 4.5˜8.7˜12.9 F_(NO) = 2.8˜3.9˜5.0 2ω = 58°˜32°˜21.9° p = 3.0 μm d =5.0 r₁ = 21.9050 d₁ = 1.0000 n_(d1) = 1.79952 ν_(d1) = 42.22 r₂ = 5.4876d₂ = 1.9041 r₃ = 133.8501 d₃ = 0.9000 n_(d2) = 1.79952 ν_(d2) = 42.22 r₄= 12.6430 d₄ = 0.2000 r₅ = 7.5698 d₅ = 1.5775 n_(d3) = 1.84666 ν_(d3) =23.78 r₆ = 19.3947 d₆ = (Variable) r₇ = ∞ (Stop) d₇ = 1.0000 r₈ =11.9178 (Aspheric) d₈ = 1.6467 n_(d4) = 1.58913 ν_(d4) = 61.14 r₉ =−11.0083 d₉ = 0.3000 r₁₀ = 3.5308 d₁₀ = 1.5734 n_(d5) = 1.72916 ν_(d5) =54.68 r₁₁ = 7.2012 d₁₁ = 0.5000 n_(d6) = 1.80518 ν_(d6) = 25.42 r₁₂ =2.5388 d₁₂ = (Variable) r₁₃ = −24.9058 d₁₃ = 2.0739 n_(d7) = 1.58913ν_(d7) = 61.14 r₁₄ = −5.9760 (Aspheric) d₁₄ = 0.5000 r₁₅ = ∞ d₁₅ =0.8000 n_(d8) = 1.51633 ν_(d8) = 61.14 r₁₆ = ∞ d₁₆ = 1.8000 n_(d9) =1.54771 ν_(d9) = 62.84 r₁₇ = ∞ d₁₇ = 0.5000 r₁₈ = ∞ d₁₈ = 0.5000 n_(d10)= 1.51633 ν_(d10) = 64.14 r₁₉ = ∞ d₁₉ = 1.2000 r₂₀ = ∞ (Image plane)n_(g1) = 1.82355 n_(h1) = 1.83271 Δθ_(RN1) = −0.0060 n_(g2) = 1.82355n_(h2) = 1.83271 Δθ_(RN2) = −0.0060 n_(g3) = 1.89419 n_(h3) = 1.91428Δθ_(RN3) = +0.0174 n_(g4) = 1.60103 n_(h4) = 1.60535 Δθ_(RN4) = −0.0018n_(g5) = 1.74570 n_(h5) = 1.75173 Δθ_(RN5) = −0.0086 n_(g6) = 1.84729n_(h6) = 1.86494 Δθ_(RN6) = +0.0158 n_(g7) = 1.60103 n_(h7) = 1.60535Δθ_(RN7) = −0.0018 n_(g8) = 1.52621 n_(h8) = 1.52977 Δθ_(RN8) = −0.0024n_(g9) = 1.55843 n_(h9) = 1.56226 Δθ_(RN9) = −0.0045 n_(g10) = 1.52621n_(h10) = 1.52977 Δθ_(RN10) = −0.0024 Zooming Spaces f 4.5 8.7 12.9 d₆11.0529 3.9900 1.5000 d₁₂ 3.0000 7.7712 12.5423 Aspherical Coefficients8th surface K = 0.0000 A₄ = −6.2411 × 10⁻⁴ A₆ = −8.9699 × 10⁻⁷ A₈ =−2.7168 × 10⁻⁸ A₁₀ = 5.6463 × 10⁻⁹ 14th surface K = 0.0000 A₄ = 1.3371 ×10⁻³ A₆ = −3.0850 × 10⁻⁵ A₈ = 1.0398 × 10⁻⁹ A₁₀ = 1.5028 × 10⁻⁷

For the filter used with the image pickup system of the presentinvention and having such an infrared cutoff function as shown in FIG.65, for instance, a 27-layered IR cutoff filter having such spectralcharacteristics as shown in FIG. 82 may be used. Set out below are dataabout such multilayered coating. This filter comprises a plane-parallelplate substrate having a refractive index of 1.52, on which 27 layers ofAl₂O₃, TiO₂ and SiO₂ are laminated in the following order. Designwavelength λ is 780 nm. Film Order Thickness Relative Substrate MaterialThickness To λ/4  1 Al₂O₃ 58.96 0.50  2 TiO₂ 84.19 1.00  3 SiO₂ 134.141.00  4 TiO₂ 84.19 1.00  5 SiO₂ 134.14 1.00  6 TiO₂ 84.19 1.00  7 SiO₂134.14 1.00  8 TiO₂ 84.19 1.00  9 SiO₂ 134.14 1.00 10 TiO₂ 84.19 1.00 11SiO₂ 134.14 1.00 12 TiO₂ 84.19 1.00 13 SiO₂ 134.14 1.00 14 TiO₂ 84.191.00 15 SiO₂ 178.41 1.33 16 TiO₂ 101.03 1.21 17 SiO₂ 167.67 1.25 18 TiO₂96.82 1.15 19 SiO₂ 147.55 1.05 20 TiO₂ 84.19 1.00 21 SiO₂ 160.97 1.20 22TiO₂ 84.19 1.00 23 SiO₂ 154.26 1.15 24 TiO₂ 95.13 1.13 25 SiO₂ 160.971.20 26 TiO₂ 99.34 1.18 27 SiO₂ 87.19 0.65 Air

Values for conditions (41) to (45-5) and other parameter values in theaforesaid embodiments and examples A′ to G′ are given below. Example A′Example B′ Example C′ Example D′ (41) p/d 5.72 × 10⁻⁴ 3.55 × 10⁻⁴ 5.72 ×10⁻⁴ 3.18 × 10⁻⁴ or 4.52 × 10⁻⁴ Example E′ Example F′ Example G′ 4.88 ×10⁻⁴ 6.09 × 10⁻⁴ 6.00 × 10⁻⁴ or 4.00 × 10⁻⁴ or 3.64 × 10⁻⁴ Embodiments(for phototaking lens 301 and filter 302) (42), T₇₀₀ 0.02 (43) T₆₀₀ 0.79T₄₀₀ 0.45 (44) S₆₀₀ 66% S₆₅₀  7% S_(p) 87% (S₆₀₀ − S₆₅₀)/S_(p) 0.68(45-1) G_(p) 532 nm (45-2) Y_(p) − G_(p) 539 − 532 = 7 nm (45-3) C_(p) −G_(p) 505 − 532 = −27 nm (45-4) M_(p1) 455 nm (45-5) M_(p2) 613 nmStrength with respect to peak at 530 nm (for color filter alone) Ye M CG 0.96 0.25 0.80 0.71 FIG. 65 600-nm transmittance 96% 700-nmtransmittance  0% FIG. 82 600-nm transmittance 92% 700-nm transmittance 2%

While the present invention has been explained with reference to avariety of embodiments, it is understood that the invention is in nosense limited to these embodiments; the constructions of the aforesaidembodiments may be combined with one another or modified in variousmanners.

As can be seen from the foregoing explanations, the present inventioncan provide an image pickup system and an image pickup optical systemwhich, albeit being simplified in construction, enable the images of awide range of natural subjects to be satisfactorily reproduced withsubstantially reduced color flares.

1-41. (canceled)
 42. An image pickup optical system for forming asubject image on an electronic image pickup device, wherein: λ1 existswithin a wavelength range of d-line or shorter, and a wavelength λ cwhose transmittance is a half value of d-line transmittance satisfiesthe following condition (14).λ≦λc≦d-line (587.56 nm)  (14) where λ1 satisfies the following condition(13):(Lλ−Ld)/F _(min)=0.05 mm  (13) where F_(min) are the minimum F-number ofsaid optical system, and Lλ is the absolute value of sphericalaberrations for a marginal ray at an arbitrary wavelength λ and Ld isthe absolute value of spherical aberration for a d-line (587.56 nm)marginal ray when the F-number is F_(min).
 43. An image pickup opticalsystem for forming a subject image on an electronic image pickup device,wherein: λ2 exists within a wavelength range of d-line or shorter, and awavelength λ c whose transmittance is a half value of d-linetransmittance satisfies the following condition (16):λ2≦λc≦d-line (587.56 nm)  (14) where λ2 is a wavelength satisfying thefollowing condition (15):|Sλ|=0.025 mm  (15) where S λis the amount of transverse chromaticaberration of magnification for an arbitrary wavelength λ with respectto d-line (587.56 nm) at an image height ratio of 0.9 with respect tothe maximum image height.
 44. An image pickup optical system for forminga subject image on an electronic image pickup device, wherein: λ1satisfies the following condition (18), and a wavelength λ c whosetransmittance is a half value of d-line transmittance satisfies thefollowing condition (17):390 nm≦λc≦440 nm  (17)390 nm≦λ≦430 nm  (18) where λ1 is a wavelength satisfying the followingcondition (13):(Lλ−Ld)/F _(min)=0.05 mm  (13) where F_(min) are the minimum F-number ofsaid optical system, and Lλ is the absolute value of sphericalaberrations for a marginal ray at an arbitrary wavelength λ and Ld isthe absolute value of spherical aberration for a d-line (587.56 nm)marginal ray when the F number is F_(min).
 45. An image pickup opticalsystem for forming a subject image on an electronic image pickup device,wherein: λ2 satisfies the following condition (17), and a wavelength λcwhose transmittance is a half value of d-line transmittance satisfiesthe following condition (19):390 nm≦λc≦440 nm  (17)390 nm≦λ2≦430 nm  (19) where λ2 is a wavelength satisfying the followingcondition (15):|Sλ|=0.025 mm  (15) where Sλ is the amount of transverse chromaticaberration of magnification for an arbitrary wavelength k with respectto d-line (587.56 nm) at an image height ratio of 0.9 with respect tothe maximum image height.
 46. An image pickup optical system for forminga subject image on an electronic image pickup device, wherein: λ1satisfies the following condition (20) as well as the followingconditions (21) and (22):,350 nm≦λ1≦550 nm  (20)τ(λ1)≦10%  (21)τ(λ1+30)≧50%  (21) where λ1 is a wavelength satisfying the followingcondition (13):(Lλ−Ld)/F _(min)=0.05 mm  (13) wherein F_(min) are the minimum F-numberof said optical system, and Lλ is the absolute value of sphericalaberrations for a marginal ray at an arbitrary wavelength λ, and Ld isthe absolute value of spherical aberration for a d-line (587.56 nm)marginal ray when the F number is F_(min), and τ(λ1) represents thetransmittance ratio of the image pickup optical system at the wavelengthλ1 with respect to d-line transmittance, and τ(λ1+30) represents thetransmittance ratio of the image pickup optical system at a wavelengthλ1+30 nm with respect to d-line transmittance.
 47. An image pickupoptical system for forming a subject image on an electronic image pickupdevice, wherein: λ2 satisfies the following condition (23) as well asthe following conditions (24) and (25):350 nm≦λ2≦550 nm  (23)τ(λ12)≦10%  (24)τ(λ2+30)≧50%  (25) where λ2 is a wavelength satisfying the followingcondition (15): |Sλ|=0.025 mm  (15) wherein Sλ is the amount oftransverse chromatic aberration of magnification for an arbitrarywavelength λ with respect to d-line (587.56 nm) at an image height ratioof 0.9 with respect to the maximum image height, and τ(λ12) representsthe transmittance ratio of the image pickup optical system at thewavelength λ2 with respect to d-line transmittance, and τ(λ2+30)represents the transmittance ratio of the image pickup optical system ata wavelength λ2 +30 nm with respect to d-line transmittance.
 48. Theimage pickup optical system according to claim 43, wherein saidcondition (13) is replaced by the following condition (13′):(Lλ−Ld)/F_(min)=0.04 mm  (13′)
 49. The image pickup optical systemaccording to claim 43, wherein said condition (13) is replaced by thefollowing condition (13″):(Lλ−Ld)/F _(min)=0.04 mm  (13″)
 50. The image pickup optical systemaccording claim 43, wherein said condition (15) is replaced by thefollowing condition (15′):|Sλ|=0.02 mm  (15′)
 51. The image pickup optical system according toclaim 43, wherein said condition (15) is replaced by the followingcondition (15″):|Sλ|=0.02 mm  (15″)
 52. An image pickup optical system forming a subjectimage on an electronic image pickup device, wherein by satisfying thefollowing condition (26), with a wavelength kc whose transmittance is ahalf value of d line transmittance, satisfying the following condition(27):(Lg−Ld)/F _(min) ×τh≦(Lg−Ld)/F _(min) ×τg  (26)h-line (404.7 nm)<λc<g-line (435.8 nm)  (27) where F_(min) representsthe minimum F-number of the image pickup optical system, and Lhrepresents the absolute value of the amount of spherical aberration foran h-line (404.7 nm) marginal ray, Lg represents the absolute value ofthe amount of spherical aberration for a g-line (435.8 nm) marginal rayand Ld represent the absolute value of the amount of sphericalaberrations a d-line (587.56 nm) marginal ray when F-number is F_(min),and τh represents the h-line transmittance of the image pickup opticalsystem with respect to d-line and τg is the g-line transmittance withrespect to d-line.
 53. An image pickup optical system forming a subjectimage on an electronic image pickup device, characterized wherein bysatisfying the following condition (28), with a wavelength λ whosetransmittance is a half value of d-line transmittance satisfying thefollowing condition (27):|Sh|×τh≦|Sg|×τg  (28)h-line (404.7 nm)<λc<g-line (435.8 nm)  (27) where Sh represents theamount of transverse chromatic aberration of magnification for h-line(404.7 nm) with respect to d-line (587.56 nm) at an image height ratioof 0.9 with respect to the maximum image height, Sg represents theamount of transverse chromatic aberration of magnification for g-line(435.8 nm) with respect to d-line (587.56 nm) at an image height ratioof 0.9 with respect to the maximum image height, τh represents theh-line transmittance ratio of the image pickup optical system withrespect to d-line and λg represents the g-line transmittance ratio withrespect to d-line.
 54. The image pickup optical system according claim42, wherein coating films for correcting wavelengths are applied onplanes.
 55. The image pickup optical system according to claim 42,wherein a low pass filter is located therein and a wavelength-correctingcoating is applied on at least one surface of said low pass filter. 56.The image pickup optical system according to claim 42, wherein aninfrared cutoff filter for reducing an infrared light component islocated therein and a wavelength correcting coating is applied on atleast one surface of said infrared cutoff filter.
 57. The image pickupoptical system according to claim 42, wherein coating is carried out insuch a way that the wavelength whose transmittance is a half value ofd-line transmittance exists between g line and h-line, and between 600nm and 700 nm.
 58. The image pickup optical system according to claim42, wherein an optical path splitter means is located in an optical pathof the image pickup optical system to locate a wavelength correctingelement on only an optical path side, which has an image pickup areawhose g-line sensitivity is 300 or more of e line sensitivity and ispositioned on the side of the image pickup device.
 59. The image pickupoptical system according to claim 58, wherein an observation opticalpath leading to an observer's eyeball is defined by one of optical pathsobtained by said optical path splitter means.
 60. The image pickupoptical system according to claim 58, wherein image pickup elementshaving different spectral sensitivity characteristics are separatelymounted on some of optical paths obtained by the optical path splittermeans, and said wavelength correcting element is located on only anoptical path, side; which has an image pickup area whose g linesensitivity is 30% or more of e-line sensitivity and is positioned onthe side of the image pickup elements.
 61. An image pickup opticalsystem for forming a subject image on an electronic image pickup device,wherein by having an optical path with a light quantity control elementbeing located therein so as to carry out wavelength correction in such away that the sensitivity of said element to a wavelength between g-lineand h-line is a half value of e-line transmittance.
 62. The image pickupoptical system according to claim 42, wherein the optical element takingpart in the determination of a focal length in said image pickup opticalsystem is made up of an optical element making use of a refractionphenomenon alone.
 63. The image pickup optical system according to claim42, wherein an electronic image pickup device having three or moredifferent spectral sensitivity characteristics so as to obtain a colorimage is located at a back focal position of said image pickup opticalsystem.
 64. The image pickup optical system according to claim 42,wherein at least one of the three or more different spectral sensitivitycharacteristics the electronic image pickup device has so as to obtain acolor image has two high peak wavelengths, between which there is awavelength having a 50% or less sensitivity to both peak wavelengths.65. An electronic image pickup system comprising an electronic imagepickup device including a plurality of pixels having three or morespectral characteristics and an image pickup optical system for forminga subject image on the image pickup surface of the electronic imagepickup device, wherein: said image pickup optical system satisfies thefollowing conditions (31) and (32):(Lh−Ld)/F _(min)≦0.07 mm  (31)|Sh|≦0.04 mm  (32) where F_(min) is the minimum F-number, Lh is theabsolute value of the amount of spherical aberrations for an h-line(404.7 nm) marginal ray and Ld is the absolute value of the amount ofspherical aberrations for a d-line (587.56 nm) when said optical systemis focused on an infinite object point with F-number ═F_(min), and Sh isthe amount of transverse chromatic aberration of magnification forh-line with respect to d-line at an image height ratio of 0.9, 0.7 and0.5 with respect to the maximum image height.
 66. An electronic imagepickup system comprising an electronic image pickup device including aplurality of pixels having three or more spectral characteristics toobtain a color image and an image pickup optical system for forming asubject image on the image pickup surface of the electronic image pickupdevice, wherein: said image pickup optical system satisfies thefollowing conditions (33) and (34):(Lh−Ld)/F _(min≦)6P  (33)|Sh|≦5P  (34) where P is the minimum pixel pitch, F_(min) is the minimumF-number, Lh is the absolute value of the amount of sphericalaberrations for an h-line (404.7 nm) marginal ray and Ld is the absolutevalue of the amount of spherical aberrations for a d-line (587.56 nm)when said optical system is focused on an infinite object point withF-number=F_(min), and Sh is the amount of transverse chromaticaberration of magnification for h line with respect to d-line at animage height ratio of 0.9, 0.7 and 0.5 with respect to the maximum imageheight.
 67. The electronic image pickup system according to claim 66,wherein by satisfying the following conditions (35) and (36):(Lh Ld)/F _(min)>0.5P  (33)|Sh|≦5P  (34)
 68. The electronic image pickup system according to claim65, wherein the said condition (31) is replaced by the followingcondition (31′):(Lh−Ld)/F _(min)≦0.05 mm  (31′)
 69. The electronic image pickup systemaccording to claim 65, wherein the said condition (31) is replaced bythe following condition (31″):(Lh−Ld)/F _(min)5≦0.03 mm  (31″)
 70. The electronic image pickup systemaccording to claim 65, wherein the said condition (32) is replaced bythe following condition (32′):|Sh|≦0.03 mm  (32′)
 71. The electronic image pickup system according toclaim 65, wherein the said condition (32) is replaced by the followingcondition (32″):|Sh|≦0.02 mm  (32″)
 72. The electronic image pickup system according toclaim 65, wherein said image pickup optical system comprises a stop anda lens system portion located on an image side with said stop comprisesthree lenses or, in order from an object side thereof, a negative lens,a positive lens and a positive lens.
 73. The electronic image pickupsystem according to claim 72, wherein said negative lens and saidpositive lens located on the object side are cemented together.
 74. Theelectronic image pickup system according to claim 66, wherein said imagepickup optical system comprises a stop, and a lens system portion on animage side with respect to said stop comprises three lenses or, in orderfrom an object side thereof, a positive lens, a positive lens and anegative lens, with a positive lens group located on an image side ofsaid three lens arrangement.
 75. The electronic image pickup systemaccording to claim 74, wherein of said positive lenses, the lens locatedon the image side is cemented with said negative lens.
 76. Theelectronic image pickup system according to claim 65, wherein bycomprising, in order from an object side of the system, a first grouphaving positive refracting power, a second group having negativerefracting power, a stop, a third group having positive refracting powerand a fourth group having positive refracting power, said third groupcomprising two or less lenses or, in order from an object side thereof,a positive lens and a negative lens.
 77. The electronic image pickupsystem according to claim 76, wherein said third group comprises adoublet consisting of one positive lens and one negative lens.
 78. Theelectronic image pickup system according to claim 76, wherein a vitreousmaterial with anomalous dispersion ΔθgF>0.027 is used for the positivelens in said fourth group and a vitreous material with anomalousdispersion ΔθgF<0.01 is used for the negative lens.
 79. The electronicimage pickup system according to claim 65, wherein said image pickupoptical system comprises, in order from an object side of the opticalsystem, a front group comprising a negative meniscus lens convex on anobject side thereof, a stop and a rear group having positive refractingpower, with said rear group having at least one aspherical surface andat least one positive lens satisfying the following conditions (37) and(38).ΔθgF(r)>0.025  (37)−0.5<(R1+R2)/(R1−R2)<0.5  (38) where ΔθgF(r) is the anomalous dispersionof a medium of at least one positive lens in the rear group, and R1 andR2 are the radii of curvature on the object and image sides of at leastone positive lens in the rear group, respectively.
 80. The electronicimage pickup system according to claim 79, wherein said rear groupfurther comprises a positive lens whose medium has a refractive indexhigher by 0.17 than the d line refractive index of a medium of said atleast one positive lens in said rear group.
 81. The electronic imagepickup system according to claim 79, wherein said rear group comprises,in order from an object side thereof, a double component consisting of anegative lens and a positive lens and a positive lens.
 82. Theelectronic image pickup system according to claim 79, wherein said frontgroup comprises two lenses or, in order from an object side thereof, apositive and a negative lens.
 83. The electronic image pickup systemaccording to claim 65, wherein by comprising, in order from an objectside thereof, a first group having positive refracting power, a secondgroup having negative refracting power and movable for zooming, a stop,a third group having positive refracting power and a fourth group havingpositive refracting, power and movable for zooming and focusing, withthe four group having at least one aspherical surface and at least onepositive lens satisfying the following conditions (39) and (40):ΔθgF(4)>0.025  (39)−0.5<(R14+R24)/(R14 R24)<0.5  (40) where ΔθgF(4) is the anomalousdispersion of a medium of at least one positive in the rear group, andR14 and R24 are the paraxial radii of curvature on the object and imagesides of at least one positive lens in the rear group, respectively. 84.The electronic image pickup system according to claim 83, wherein saidthird or fourth further comprises a positive lens whose medium has arefractive index higher by 0.17 than the d-line refractive index of amedium of said at least one positive lens in, said rear group.
 85. Theelectronic image pickup system according to claim 79, wherein the lenssystem portion on the image side with respect to said stop comprises, inorder from an object side thereof, a positive lens, a doublet lenscomponent consisting of a positive lens and a negative lens, and apositive lens. 86-106. (canceled)